Vanagon,
Interesting question, but not without a logical answer.
First, concerning the thread link noted at the end of your post - there's been a lot of research done and a lot of information "discovered" and made public since 2004. Right around that time, Bill G. was putting together his "tentative" history of H&R. We had been working together since around late 1996 or early 1997 and my collection of hardware and his research of the soft ware (catalogues and company flyers, parts lists, etc.) was beginning to bear some good solid data. Well, Bill's history underwent at least three more re-writes - all of which I had the opportunity to "edit" and finally in 2005-2006 I sent sent him over 2200 digital pictures of pieces of "hardware" with most of those being detailed close-ups and comparison shots. I had the opportunity to review and do a final edit of the "publisher's copy" after Bill's death in Jan. and there still are some unanswered questions - that is what sparked me to begin this on-line quest for more info on the SPORTSMAN revolvers.
Now, as to your question. Two possibilities come readily to mind:
1. There should be three numbers stamped into the breech face of the cylinder and the star ejector. Those three numbers should match the last three digits of the serial number stamped into the bottom side of the topstrap (remove cylinder to see those.) That number should match the "real" serial number stamped into the front strap of the grip frame, visible behind the trigger guard. If there is any mismatches, it indicates that parts were swapped from another completed gun.
2. It apparently was common practice to send H&R firearms that were defective or broken or in need of updating, back to the factory to effect those services. If all the numbers match AND you have a later model cylinder - it is probable that the gun was sent in for a cylinder repair or replacement and the factory used the parts available at the time of return to effect the repair/replacement. I'm almost certain that the factory tech/smith, who would have replaced the cylinder would have stamped the last three digits of the frame serial number into the replacement parts. I KNOW for a fact that this was done with the Single Shot Target USRA Model 195 pistols. I have one that a REAL expert in H&R firearms (former QC employee and historian for H&R) has assessed as having made at least two trips back and possibly a third, for upgrading. A thought in favor of this solution is that with the introduction of HIGH SPEED .22 lr cartridges (all smokeless powder loads) in the early 1930s, an event that sparked the need for the safety rim on the cylinder of H&Rs and other "safety" features on other manufacturers' .22 revolver, resulted in many blown head cases. It is possible that the older cylinders would be swapped out for a newer cylinder in the interest of safety.
We know that the "major" manufacturers would do in-house repairs and replacements, it is inconceivable that the "minors" would not do the same. Just out of curiosity, remove the monogrip and look at the sides of the grip frame - do you see an X or asterisk (*) stamped into it on left or right side?
I'm waiting to hear about your serial number matches, before I go off on any other flights of fancy.
The least likely explanation, to my way of thinking, is that H&R used older, left over parts in newer production, mixing them - least likely because I think the demand for the SPORTSMAN grew very rapidly after its introduction and I doubt that many frames or barrel assemblies would have remained partially assembled or as loose parts in bins for those intervening years.
What do you think?