The H&R FOLDING MODEL was made in two frame sizes, Large and small and two variations of each. 1st Variation circa 1925 to 1931 with extractor and 2nd Variation 1931 - 1942 with auto ejector.
Serial numbering seems to be somewhat inconsistent. My small frame .410 which is a fairly early 1st Var. has no letter prefix. My large frame which seems to be a mid range 2nd Variation has an 'F' prefix to the serial number.
I also have several HAMMERLESS models which used an 'H' as a model designator. The latest one was made in 1941 and has a 'B' prefix before a larger 'H' followed by the numerical part of the s/n. It is entirely possible and probable that H&R would put their date designator (starting in 1940 with 'A') before the serial number, either in conjunction with the model designator or not.
Value will depend upon condition, but this model is not all that often seen for sale. Here's what I put in the 32nd Ed. of "THE BLUE BOOK..." by Fjestad for average RETAIL values:
100% (NIB) - $375; 98% - $325; 95% -$285; 90% - $235; 80% - $210; 70% - $175; 60% - $150. There is collector interest in this model.