Re: P 38
A bit of a technicality, but 135 was the number assigned to the officer who was head of the WaffenAmt (Weapons Office) inspection team at Mauser. He obviously didn't personally inspect all the weapons Mauser made but he was the team commander and administrator and was ultimately responsible for production and quality.
That gun appears to be all matched and in good shape; my WAG at retail value would be $700 or so.
If you ever need to identify that pistol for your records or any legal purpose, complete and unambiguous identification would include the maker, year, number and the suffix letter: P.38, byf (Mauser) 1944, serial number 1625 t.