Hello Again:
Sorry that I wasn't able to get back sooner. Thank you for the additional photos. They help clarify things … a little. First, let me explain that I'm not an expert. The best source of information on lugers is Jan Still's Luger forum. My knowledge comes from fifty years of admiring lugers and reading everything that I can such as the stuff posted on Mr. Still's forum and in books. So, with that little disclaimer, here is what I think that I can offer. As we said before, your luger was made for the German military by DWM in 1914. You've told us that the serial numbers all match but the "numbers" are only part of the serial number. On the frame, immediately under the barrel the entire serial number is stamped and it will be a serials of number followed by a suffix "letter". That letter is part of the serial number. The contract specified that each pistol would be stamped with a number, presumably from 1 to 9999 and then the numbering would start over again with "1a" and so on through the year and then begin again the next year all over again at 1. So, each year there were "series" of lugers made - an "a" series, a "b" series or block, and so on. Some times folks, even dealers, will say that they have a really "rare early" luger, for example, serial number "12", but when you look closer it is serial number "12t", meaning that it was the 12th luger in the "t" series or block of numbers for that year. I don't know when in 1914 your luger was made, but the letter suffix will give you a better idea.
The other marks tell us things too, but everybody isn't in complete agreement on what exactly they tell us. For example, those little stamps on the right side of the receiver are inspection marks. Some folks contend that the the letters under the little crown are the initial of the last name of the inspector, with the "x" being used by a junior inspector whose last name initial was already in use by a senior inspector. The little eagle which is last in line is the military acceptance stamp, sometimes called the "Reichsadler" or "kings eagle."
The stamp "Bo 30" on the bottom of the barrel is a reference to the kind of steel used in the barrel. In this case, it is "Bohler Steel 30". Bohler Steel is still in business today.
The stamp "8.83" is the exact measurement of the inside of the barrel, meaning that it is within the specifications for 9mm.
The markings on the grip strap were unit markings, but unfortunately they have been damaged to the point we can't determine which unit used your luger. The most frequently used "P…" units were police units. Many of the police marked pistols started life as military pistols but at the end of the war were turned in by the military and "reissued" to the police. When this happened the pistols typically would be stamped with the police unit designation. Your example does not show any of the other indications that it is/was a police reissue. For example, your luger does not have the "police safety" or the 1920 stamp on the receiver typical of so many reissued police lugers. There were regular army units that began with "P…" such as "Pioneer," "Proviant" (meaning provisions), "Park" (meaning depot), "Pferd" (meaning horse). If the next letter was a "U" as you indicate, that narrows it a little more because there were fewer "U"s. The "U" could mean Ulanen (a type of kavallerie), unterofficier school (nco school) or some other unit unknown to me. At this point, I can't think of any units that would begin "P.U…." at least according to the official way of designating units. However, these stamps were generally applied by the units themselves and the folks who actually did the stamping did not allows follow the "official" rules. The folks over on Jan Still's forum could offer more.
Lieferungsgenossessenscahft der Sattler (LGS) began in Nürnberg in March 1915 as a union of three small leather goods companies. So your holster was probably made a little after your pistol. They made cartridge boxes and bayonet frogs as well. The company went out of business in 1969. If you do an internet search for "Lieferungs genossenschaft der Sattler Nürnberg" you'll find all sorts of stuff. I do not know what the "28" means, but it could indicate any number of things--pistol number, replacement number, etc. There may be some more numbers and/or letters stamped in ink under the flap of the holster. There should also be a little pouch for the loading tool under the flap as well. A genuine, WWI loading tool can be found on fleabay for $50-$100. Holsters such as yours range from a low of about $100 to as high as $250, depending on condition, markings, and whether the loading tool is present and original. (Some folks are asking as much as much as $35.00 for reproduction loading tools.)
The alum. based magazine has the serial number with the letter suffix, but it also has the little "+" sign. That usually means that it was the second magazine for the pistol with that serial number. The fact that this example has the alum. base but no waffenamt suggests that it might have been made for a Weimar era luger (1920-1933). The alum. base with the blued body was typically issued until about 1939, but after 1933 they had the waffenamt. You will find magazines like this one for sale anywhere from $100 to $150. The price would be slightly higher for one with the waffenamt.
Finally, the question of whether or not it has been refinished. Lots of lugers just like this were imported into the US in the period from about 1950 to about 1965. They sold for as little as $35.00 and for three or four dollars more you get one one that had been "arsenal refinished." A holster like yours would be purchased for another $4.00 or $5.00. Look at where the file or grind marks on the grip strap. If you see shinny metal, it may be only one finish (the original finish). If there is not shinny metal and you can see blued finish over the grind/file marks, it has been refinished. Sometimes you can actually see the two different colors of finish if the unit mark was filed after it had been refinished. Where does all of this leave us with "value"?
Lots of guys who bought these pistols in the period 1955-68, bought them because they wanted a souvenir of their service in WWII. When the pistol arrived and it wasn't a "Nazi" luger like they had seen in Europe and wanted, many of them were a little disappointed. They didn't know what that stamp on the front strap was, but they knew it wasn't typically on the "Nazi" lugers, so they filed or ground them off. Some of the importers had them filed off after they discovered that many of the ex-G.I.s who bought them, didn't like them. Even today, every once in a while I will find somebody who thinks those are "import marks" and therefore not desirable. If you look over the lugers currently available for sale, you'll find examples with the unit marks ground off. What impact does that have on the price? Well, there is no hard and fast rule, but it would have been more valuable if it were still there. Lots of people don't even know what they are so it devalues the gun only slightly; others just think that it's another sort of "blemish" that devalues the gun more significantly; others collect only unit marked guns and therefore wouldn't be interested in this one at all because it's been filed. If I saw this luger, with the holster, listed on one of the internet auction sites, I would not be surprised to see it listed to start at $1000.00 with an undisclosed reserve. It could get no bids or it could sell for as much as $1500.00 or more if two guys decide they don't want the other one to get it.
I hope this helps.