The No 4 came out first, in 1899, used type 103 film, and had no door on the front, then they added the door in 1900, but still called it a No. 4 with no letter. Also in 1900 the No 1, with no letter, came out using 105 film . . . 105 was the same size as 120 film, but had smaller holes in the spools, which is why 120 film spools are a bit wobbly in these cameras. Both models opened for film loading and unloading by splitting the case into 2 pieces along a curved joint. Both the early #1 and #4 had Rapid Rectilinear lens as standard equipment, but some could be special ordered with early Goerz pre-Dagor lenses.
The Panarams went through B and C versions which were substantially the same as the original except the lens was changed to a meniscus lens and various other minor changes such as adding 3 metal plates on the sides of the film track to help keep the film from jumping out of the track, placement of the bubble level, etc.
Then, somewhere in the 1920's the D version came out which dispensed with the 2 piace case in favor of a case which opened by the back hinging downward and the sides swinging outward which exposed the insides for film loading and unloading (on the film winder side, the carrying strap had to be unclipped from the top of the camera so that side could swing open).
There were variations in the #1 & #4 D versions, as well. Some had two levels and tripod mounting threads, on on top and one on the side, so the camera could take horizontal or vertical (such as of a waterfall or tall building) shots. Some had a gear-ratchet speed control mechanism located on the bottom of the swivel lens shaft.
Lastly, near the end of Panoram production, the 3A model (the only Panoram using the A letter designation) was produced for about 2 years between 1926 - 1928. It was similar to the #1D & #4D except that it used type 122 film and many (if not all) had a 2 position speed changing lever separate from the tensioning lever.
Some of the other folks on here may have more specifics to add, especially dates/years regarding when these various iterations in the Panoram cameras occurred.