I am well aware what a time signature is. What I’m saying is that a lot of FoF charters only chart guitar, so they time signatures are sometimes altered so that the guitar notes line up on measure lines. A common example is when the guitar part has some slight overlap either from one section to the next or after a solo. Many FoF charts will extend the measure to encompass all of the note. What happens then is that a crash or something on drums that denotes the start of a measure is a couple beats early.
Yeah, I know. What I mean is that they didn’t use the time signature for guitar, which doesn’t exist, they used whatever combination of BPM and time signatures that made the notes line up nicely, completely fudging the tempo map. So yeah, sometimes you just need to ditch those time signatures and do your own, that’s the moral of the story, as you were pointing out. Something you should do, as you probably know, before doing any vocals because otherwise it will all get messy.