It could be possible to know if Pwnage 101 had the Y letter in his avatar, only if he had it when
@Third_World_Detractor scraped the data and if he got the link to his PFP image then. This is because I think Youtube does not immediately get rid of the image when you change it, it just updates it so the old link still shows the old picture.
Unless I'm making a mistake I think Youtube does this, or used to do it. As an example, this is
@Anony 's old PFP that should've been erased but it's not.
https://yt3.ggpht.com/ytc/AAUvwnj3q1kmv49I3wCdNGGDyiF1Y0_HQn43v6nWNLDT=s88-c-k-c0x00ffffff-no-rj
I need to test this to be completely sure though.
Also, like you've mentioned, there are a couple more accounts that appear to be deleted in Third_World_Detractor's second file. Have in mind that these profiles could be restored at some point.