I don't think it would be easy or even possible to have a fool proof way of detecting whether the hack has correct custom music implementation as there are many versions of Addmusic (Carol's, Romi's, HuFlungDu's, AddmusicM, Java Addmusic, whatever was used to insert music in VIP 3 and even more) with a lot of them lost to time. There's also the fact that while not broken versions of Addmusic have existed for a while now (as in they didn't put valuable data in the echo buffer) AddmusicK was the first one to not allow the user to insert a song with echo buffer set to a value that's too big, so certain hacks using the same tool work while others don't. And then there's the SMAS music patch of which I've seen one version that inserted some music data into the echo buffer.
I also have a question, how exactly would you even determine whether the Addmusic checks should be ran by BSNES?
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