Though Barclay also was a Lt. junior grade for an impossibly long time as well.
Weird how that happens in Trek. People either are promoted too quickly or too slowly. Not to mention there are too many people of officer rank to begin with.
He showed up in 2366 on the Enterprise-D as a Lieutenant jg. By 2376 when he showed up on Voyager he was a full lieutenant. Heck, he might've been full lieutenant by 2373 in First Contact, we didn't actually see him in uniform.
So ten or so years is a long time, but yeah... Reg was screwing up a lot with his holo addictions, and severe phobias so often getting in the way of his work. It stands to reason once he became more steady... as was described in the Endgame future, he could start working his way up the ranks again.
Either way, it's perfectly concievable that Chakotay steadily rose up the ranks even if he didn't do much to "get noticed." I always liked to think that the "lieutenant commander in Starfleet" who resigned on principle who was her instructor at Advanced Tactical that Ro mentioned in Preemptive Strike was Chakotay.
Charles Phipps wrote:
I felt that episode would have been more interesting if Picard had found out being a Lieutenant Junior Grade with an area of special concern (say, cosmic dust) allowed him to have a family and Mediocre Picard was actually fairly happy.
It makes sense in an integrated NASA-like group that the posts normally held by civilians get ranks.
That might have been interesting. Both the civilian honorary rank bit and the happy family part. Though over all I think it would've distracted from the over all theme of the episode and clouded the issue.