Rule variations between PF1/3.5 - Stacking

[glass]

https://srd.dndtools.org/srd/classes...oogle_vignette

Fair enough. The rest of your post was talking about Pathfinder, so I thought you meant the Pathfinder Ninja (and TBH, I had forgotten the 3.5 Ninja existed).

You can definitely add constant numbers to your armour class (or attack bonus or whatever) more than once, so why would you not be able to add variable bonuses more than once? For example, a manifested ghost with battle dancer levels should add its charisma to its armour class twice, once as a deflection bonus and once as an untyped bonus.

"A deflection bonus equal to your Charisma bonus" and "your Charisma bonus" are not the same thing. You could have 1000 of the former, but you would only get the benefit of one due to the stacking rules. You can only ever have one of the latter, so there is no need to invoke the stacking rules.