True. It just seemed to get more noticeable around the time The Soul Key came out. I think a big part of the reason for that was in TNG/Titan timely Ezri was captain of her own starship, while in The Soul Key she was still on DS9 as a Commander (or was it Lt. Commander, I forgot). After that it seemed they started doing more crossovers, in fact I think it was a while before we got a DS9 novel that actually carried the DS9 logo. But if they wanted to do more crossovers then I guess it made sense to bring it up to the same time period as TNG/Titan.
Voyager was interesting. When Beyer took over that line from Christie Golden she brought it pretty close to the time period TNG was, but then they fell behind again. Though in that case it didn't seem to matter as much since the crossovers didn't involve Voyager at all. I think the only thing that seemed to crossover was when Tuvok joined the Voyager fleet for a period of time. Like I said, it'll be interesting to see if any of the ships or characters from Voyager appear in Coda or if we find out how things eventually turned out, since TNG/Titan/DS9 are several years in the future last we saw.