Here's my thoughts on the design and genesis of the Colts revolver:
1851 Navy came first in 36 calibre.
Then more power was needed so the frame was rebated, cylinder enlarged (where it could be allowing the frame to use all the same geometry and parts). This was fine in concept for loose charges as the additional material in the front section of the enlarged cylinder gave added strength so larger barrel design and away we go for about 10 years.
I have heard it said that Samuel was a negative Nancy about cartridge pistols and shunned Rollin and White's invention, which they patented, so the company, after his death, played catchup with their designs.
The Thuer was first and not really successful for it's cartridge design and was soon unnecessary as Grant did not renew Rollin and White's patent so Colt then applied the concept to their existing designs.
This creates a number of "work arounds" which Colts accomplished by making huge changes to the revolver. The 1851 Navy has plenty of working room in the design but the already taxed 1860 Army gets very close to the design limitations. Eventually Colts moves onto a newer design eliminating the frame modifications with the advent of the 1871/72 open top. The Open Top, in very short order, becomes obsolete with the advent of centerfire ammunition so they design the 1873 SAA Army revolver.