> A couple: usually 2, though not always

I had to explain this to my German friend. In my understanding this isn't about the actual number, it's about the certainty. If it's absolutely and definitely two, then I say two. If I'm uncertain but it's probably two, or if a non-integer, somewhere around two, then I say couple.

And few is more likely to be 3 than 5, because 5 is getting close to a "half-dozen or so", or (as you say) several.

Many is very context-sensitive, as the meme has it.

So I would agree that the open models are a few months behind, definitely more than a couple of months behind, possibly several months behind, maybe a half-dozen months or so behind, but not many months behind.

Several and a few are the same number, they only differ rhetorically.