Corona D55= Sitka Bracing, Grover Rotomatic closed back tuners, Sitka top, EIR back and sides, Slightly different body shape than the New Hartford Models with more sloped shoulders and less of a waist, Black composite headstock overlay, Ebony Bridge and fretboard, Heavier Build, a bit thicker neck profile with almost 1.75" nut width (at least on mine anyway), thicker Nitro Finish, Non compensated bone saddle and Bone nut. I am pretty sure the factory add on electronics were a 9 volt Fishman under saddle unit.
Here is a front shot of my 2003 50th anniversary D55 for reference. This guitar has an Englemann Spruce top instead of Sitka as it is the limited Anniversary model However it is the same shape as the regular D55's with the Stika top.
New Hartford D55= Adirondack Bracing, Gotoh 700 series open back tuners, Sitka Top and EIR back and sides, More Traditional Body shape with squared off shoulders and a more defined waist, Solid Ebony Headstock overlay, Ebony Bridge and Fretboard, Lighter Build, A bit smaller Neck profile with closer to 1 11/16" nut width on both of mine, Thinner Nitro Finish (on both of mine as well), Compensated Bone saddle with Bone nut. Factory Electronics were 18 volt DTAR Multisource with built in condenser mic.
Here is a pic of my 2014 D55-RS for reference. This was part of a 3 guitar special run with the Adirondack top but it is the same body shape as the regular Sitka topped models.
I am sure there are other differences but this is what I can think of right now. Congrats in Advance on picking up a D55 Rich! They are wonderful guitars, Hope this helps!
TX