George Steinbrenner wrote:
I don't know why people keep thinking the Eagle is Constitution class just because of the Operation Retrieve chart. The silhouette of a Connie was just used as a generic icon for any starship. The real ship doesn't have to be of that class.
I think it's because the Eagle was originally considered a Constitution class starship based on Greg Jein's starship list way back when (associated with registry 1685 on that list). I'm pretty sure those who made the operation retrieve chart weren't thinking "hey that ship is supposed to be a connie with a registry of xxxx" so they gave it a low number and yes it could technically be any ship type since we never saw it onscreen and Greg's list is not canon. However since the Eagle has been associated with the connie type and 956 isn't too far from 1017 (Constellation) which is obviously a connie (yes I know why they did that) all the evidence suggests the Constitution class starship line began pretty early in the registries 900/800/700 even? That suits me fine though as it means the first Connie's would have been built in the early 23rd century or even late 22nd century rather than the 2240's and also why by the 24th century they were considered obsolete and phased out while the Miranda class (1800+) was still serviceable.
Also I don't believe that many other ship designs existed in the original trek series era since when it came out the only real "starship" design the creators envisioned looked just like the Enterprise. It was only in later years that the show creators added earlier ship designs like Daedalus, Oberth, Antares and NX Enterprise. So for me really any ship from ncc 700-1800 (when the Miranda line began) could most likely be a connie and while no I have no evidence it just feels right