Recognizing bootleg Spotify releases

I just added two singles for the band ZHIEND, which is a fictional band featured in the anime Charlotte. These two singles were released only on Spotify in 2020, the copyright and phonographic rights are credited just to “ZHIEND”, instead of any company or label. Most of Key’s music is not available on Spotify, so this feels all very off.

I didn’t set both singles as bootlegs because I can’t really confirm they are bootlegs with the information I’ve got at hand, so I instead left the status blank and added a note saying that these releases are “most likely unofficial”, but I was wondering how I should approach situations like this one and whether there is any way to recognize when a Spotify release is unofficial. I’ve found some live albums for some big bands that were clearly bootlegs due to the cover arts and the companies claiming copyright on them, but this is a more ambiguous case.