So, I had a problem with replays from Gensokyo's archive but I managed to solve it. However, it does raise a concern for the newer database.
The issue was that some of my IN replays weren't detected by the game after I downloaded them. After a while, I did figure out what's the deal. The replays get renamed on uploading and the name format is "th8_udAAxx", where "AA" are letters taken from the nickname and "xx" is an index number. The issue happens when that index goes above 99. The filename is formed successfully (e.g. "th8_udCL100.rpy") but it's one character too long for the game to detect it properly. Thankfully, renaming the replay makes it show up just fine (e.g. "th8_udCLA0.rpy").
tl;dr If a replay from Gensokyo's archive doesn't show up in the game just change its name so that it's one character shorter.
The concern that raises for the new database is that something like that can happen there as well. It seems to use a plain 4-digit universal index that is approaching 5000 now, and if that reaches 10000 that problem will affect all new replays. My suggestion, in case there's no failsafe in there already, is to go "Garegga scoring" route - replace top digit with a letter once index reaches 10k. It's been a while since I looked into any sort of programming, but it should be not that much of a hassle to add.
