Re: Arisaka Type 99 numbers
The Japanese, then and now, use both number systems, and there seems no real rhyme or reason as to which is used where. I know of no use of the Japanese numbering for serial numbers of weapons, but the model "Type" numbers are always Japanese.
I have never been in Japan, but have been told that it is (or at least was) common for stores to display prices in both "arabic" numbers and Japanese. The latter was a lower price and that is what you paid if you could read the Japanese numbers; if you couldn't, you paid the higher price. I laughed MAO at that story; really neat.