Question is whether certain thief skills have their effectiveness juiced when the thief goes "all the way" in that path. From the helpfile for garrotte:

The more adept the thief is as a binder, the better chance they will have with their garrotte.

What's that in reference to? Skill % at nimble fingers? Skill % at other binder skills, e.g. hands, legs, etc.? Number of skills taken in the path?

Generally, later skills in a path might offer a passive bonus to earlier skills in a path, much as later spells in an invoker path might offer passive bonuses to earlier spells in the same path.

Don't ask me which do and don't and which skills boost which other skills; I can't remember.

True for all paths or just binder?

Probably all.

And it was one of the skills specifically mentioned back then as having this sort of passive bonus. Does it still, now that it's a general skill?

Sure hope not. Because that would be super unintuitive.