A call to Colt many, many years ago about acquiring a convertible cylinder revealed that there may have been two different barrel sizes made, which I find hard to believe.
It is absolutely true. I have a scout (k-series) that is 22LR marked barrel with no conversion cylinder. Once, at a show, I mistakenly purchased a k-series that only had the magnum cylinder, and the barrel was marked 22 caliber. I concluded that I could shoot 22lr from it, but that it wasn't worth the expense to find a nickeled 22lr cylinder, so I sold the gun.