From what I understand about the Baldwin studio uprights (having looked at a lot of ebay & craigslist ads, including photos, serial numbers, etc, and seeing several in person) ...
Marketing data says they started in 1939, but I've seen one at a store in San Marcos, CA, whose serial number dated it to 1937. This early, they were labeled "Hamilton" in the center of the piece above the fallboard, and "A Product of Baldwin" to the far right and on the plate. (The same name was used some time before that, but on a different-styled piano, which may or may not have had the same plate in the mid 1930s. Earlier (1900s, 1910s, I think), the Hamiltons were tall uprights labeled as "Hamilton Piano Co" on the fallboard, with a "House of Baldwin" emblem on the plate.)
Around 1949, they introduced the full-width music desk. (Previously it only was about half the piano's width.)
Around 1951, the plate and right-side name was changed to "Built By Baldwin", while retaining "Hamilton" on the fallboard.
In 1956, the scale was changed - the piano was widened a couple inches, bass string length was increased a few inches (I measure 43" in my 1950 Hamilton and 48" in my 1956 Hamilton for the low A), and the low tenor went from plain trichords all the way to the break to having 2 wound bichords. This then-new design was the 243. (There were also other variations on the 243 later, but I don't know what's what on those, like 243E, 243HP, 243HPA, etc.) The previous scale, according to an RPT in SoCal who's known me since I was a baby, was the 242.
Around 1963, the cabinet was changed to the propstick cabinet - front and top lifts up in one piece, and a propstick swings down to rest on the left side. (Previously the top lifted up (from "catches" in the front panel), and the front panel had latches inside to remove it.)
Around 1966 or 1967, the name was changed again, this time to "Baldwin" in the center of the fallboard on a brass(?) plaque, "Hamilton" on the right, and "Baldwin Made in USA" on the plate.
Sometime in the mid 1970s or so, the design of the fallboard plaque was changed, losing the brass and making the plaque the shape of the letters. I've heard there was also a minor scale tweak in there, but I don't know any details about that.
Around 1987 I think, Del Fandrich rescaled the piano, this time with 4 bichords in the tenor above the break. (Correct me if I'm wrong, Del? I'm guessing maybe it may not have been you -- or do they have the "reverse-curve"-from-tradition bass bridge without a cantilever and a floating soundboard?)
In the early 1990s, the cabinet was returned to having the top lifting separate from the front, but without the spring-loaded "catches".
The last Baldwin studio uprights made in the USA were made around 2001 or so, I think, when Baldwin was bankrupt and bought by Gibson. Recent ones are made in China, in a factory owned by Baldwin/Gibson.
(BTW, for some time in the last decade or two, there were some pianos made with the Hamilton name on them. These are not the same as the Baldwin studio uprights we've been talking about.)
I'm sure there are plenty of technicians who worked on the original Hamiltons when they were new can chime in and correct me on what I've said.
Also, Baldwin Hamiltons are among my favorite upright pianos, especially the older ones, before about 1962, and to a lesser extent before about 1986 or so. (No, I'm not admitting to being OCD on Hamilton history. :p)