Checking on the Sylvania datasheet for the clear mercs, they say hat they are 'blacklights' when they are supposed for general illumination. I don't understand, as don't MV blacklights have the purple glass/coating? Also, they could make the glass differently, but it isn't a blacklight. How come?

"BL" mean it does emit the near UV, it does not have to be purple. "BLB" is then the "BL" with a filter blocking the visible light.
Isn't that only a workaround to the MV bans?
"Blacklight" = special purpose bulb, so rules for "general illumination" bulbs do not apply...