Here is the history if you want to better understand where Gerber comes from and how it evolved:
https://en.wikipedia.org/wiki/Gerber_format#History(Ucamco was Barco initially, and IIRC, the first version of the Gerber spec I worked with was from Barco.)
They absolutely hold the official specs, and the various revisions of the specs they edited (until X2 which brought attributes) were always clearing up elements of the previous ones that may not have been clear enough. So I definitely suggest getting ahold of the latest one - for those that have to generate or interpret Gerber files. Do not just stick to revisions that are 20 years old.
I've written two Gerber renderers, and have always based them on the Barco/Ucamco specs. Never had any issues with any files (except of course for a couple bugs that were my fault). gerbv is not a good example IMO. It sucks. It has made great progress though, but it was not that great really. Not just saying this because I wrote my own tools (even though I admit the reason I did was that there was NO proper tool available at the time), but gerbv can't blame its issues on the Ucamco specs. That wouldn't be honest. (And no I haven't released my renderers so I have nothing to sell here.
But having done that, I think I know the Gerber specs a bit better than average.)
And yes, contrary to Gerber, there are licensing problems with ODB++. I had a hard time getting ahold of the specs and I don't think I'd be allowed to used them commercially as is. It's also too much of a mess to be something nice to generate - really a pain.
IPC-2581 has failed so far, it has unfortunately gotten little traction.
My bet is that Gerber X3 is what's going to replace both, as the licensing is a no-brainer, it contains everything needed, the spec is clear, and previous Gerber revisions have already been used everywhere for a long time.