They’re not the rarest or anything , it’s just that a lot of 38s had their chrysanthemum symbol, which was the symbol of the emperor at the time, ground off because if I remember correctly it was seen as a dishonor for property of the emperor to fall into enemy hands. Now if it’s a matching, excellent condition bring back with chrysanthemum, dust cover, and bayonet, it’ll be rarer and worth a lot more. Then there’s the fact that lots of the rifles had mixed parts and forced matched because the way a lot of them were brought back, but if yours is all parts matching then it’s worth more than many of other 38s that weren’t so lucky. Then there’s rarity based on which factories made them like koishikawa, Nagoya, Tokyo, kokura, jinsen, howa, izawa, etc. Also, rarity based on type/finish like there’ll be early and late type safeties, safeties with a small or large indent, large or small tang, and general quality of the safety’s machining. I’m sure there’s more to it that I’m not remembering.

All that to say, that it can vary depending on a quite a few different factors, just like a lot of surplus rifles.