Right now the tooltips describing luxury bonuses are not at all clear.  Take "Dye" for instance:

This tooltip does not indicate if these bonuses are "per dye" or if they are flat, and extra dye doesn't provide extra bonus.  After some testing, it appears that the industry is a 'per dye' bonus, while the stability is a flat bonus (each type of luxury only provides it's stability bonus for the first time you access it).

I believe all stability bonuses work like this, but do all non-stability luxury bonuses?

Obsidian seems to imply that only some of the luxuries are 'per luxury', but I think this may be incorrect.  Either way, the tooltips need to be standardized & consistent.

Would be much more clear if when hovering over your luxury icon in the empire panel in upper right it showed you the current bonus you're getting from the current number of luxuries that you have rather than the bonus you get from just one, but I agree the detailed descriptions should be updated (here and in several other places like religious Tenets) to make clear whether bonuses stack or how they multiply together when they do stack.