(I mentioned this on Discord, thought I'd post it here too.) Eleanor Forte and Kizuna Akari were both released in 2018 and both have over 700 songs.
So it seems like they're both doing fairly well in terms of songs-per-year among newer voicebanks.
Out of the voicebanks released in the last few years, the fastest rising stars have been
v flower at an average of 570 songs per year, and Otomachi Una at an average of 660 songs per year.
Good lord, I just rediscovered these two songs from Nov-Dec 2007 by YashiroP. There isn't much info on them. As soon as I heard these I instantly recognized them. I feel like they were fairly popular when they came out, but it looks like the original reprints on YouTube are long gone. It's hard to describe what this makes me feel. Like finding a keepsake that you thought was lost. These nearly forgotten songs that I listened to so much back then.