Certainly possible. Interestingly, Eagle is a smaller silhouette than Potemkin, possibly suggesting a different ship type, which would make more sense of the registry. Three digits for scout ships came from SFTM of course, and was picked up in the films for the Grissom and Copernicus.
Good views of the original 'Operation Retrieve' chart here:
I wanted to post that here my latest replica - a half scale version of the Operation Retrieve Command Briefing briefly seen in The Undiscovered Country, but more so in a cut scene from the movie. Originally this prop was disposed of after filming wrapped, but Penny Juday (former Paramount Trek...
www.therpf.com
The Eagle NCC-956, the Emden NCC-1856, and the Ahwahnee NCC-2048 are all shown with the smaller silhouettes. Even if they were all meant to be a different class than the Constitution refit, that's quite a spread of numbers for just one specific class.
But this is what we have to work with:
1. A silhouette clearly distinguishing the Excelsior from the other ships.
2. The Endeavour and the Potemkin using the larger Constitution silhouettes on the Strike Operations chart, and the Eagle, Emden and Ahwahnee using the smaller Connie silhouettes.
3. The Potemkin, Korolev and Emden using the same size Connie silhouettes on the Theater of Operations chart.
So what are the conclusions we could possibly draw from this?
1. The silhouettes, regardless of size, do in fact represent the class of a particular ship. So other than the Excelsior, all the other ships are Connies.
2. The smaller Connie-like silhouettes represent a smaller class of ship, but then this is inconsistent with the Emden shown as smaller in one chart and the same size as the Potemkin on the other chart.
3. The silhouettes, other than the Excelsior, are just placeholders, and do not represent the ships' true class. But then why distinguish the Excelsior with its own distinct silhouette?
If I had to make an educated guess based on the evidence, I would go with Occam's Razor: #1 is clearly the simplest explanation, and all the ships other than the Excelsior are Connies. It would have been nice if they'd used, say, a Miranda silhouette for a ship or two, since then there would be no question that the silhouettes represented that specific class. But they didn't, so we have to extrapolate based on what they did do.