(I do not yet have the game, but am planning on getting it next time it goes on sale.)

So, Classic Mode has been added, and it appears that it's a separate game that plays like the older Castlevanias (not the metroidvanias that dominated the series before it petered out). This comes with many characteristics, like the fact that you can only have one sub-weapon at a time, and picking up another one will over-write the old one.

In Castlevania 1 and 3, every now and then an enemy would drip a sub-weapon and if you picked it up (very easy to do by accident, particularly if you're not paying attention or you're already in mid-air), it would replace your current sub-weapon. Naturally, this could cause problems (and has likely ruined many a speedrun attempt). Castlevania 4 got rid of this mechanic. (Castlevania 2 is too different, to the point where it could be considered a metroidvania despite it pre-dating Symphony of the Night.)

So, my question is:
* In Bloodstained's Classic Mode, do enemies ever drop sub-weapons when defeated, or does this game not have that mechanic?

I only played for a little while , but it doesn't seem that enemies drop Sub-weapons, you only get them from candles

If you pick a sub-weapon in Rondo of Blood, the old sub-weapon will fall to the ground, allowing you to pick it back.

I think I remember that in Symphony of the Night as well, and that might have carried over into Circle of the Moon and Harmony of Dissonance. (Those earlier metroidvanias still had the "one sub-weapon" rule, even though it makes less sense here (and even Castlevania 2 let you switch sub-weapons in the menu).)