> If that code existed, it would have failed, wouldn't it? So it seems
> unlikely.
Either that, or the users just did the (and ... t) trick to normalize the result themselves.
Or it failed, but very rarely. In some cases that I've fixed, the t result can be produced through many branches of an `or', for example, and most of them already returned t, but not all.
Or look at speedbar-this-file-in-vc: it had a flaw, because it promised non-nil but could in some cases return the result of `run-hook-with-args' (which is documented as having an unspecified return value). So certainly such bugs can exist and just be triggered in very unusual situations.