Oh boy, more conflicting information on the Marshall "M" suffix. If someone has seen a Marshall with the "M" suffix, I may reverse my feeling and say they all should have it. Perhaps the two in my data file are rebarreled guns like the one mentioned. I now believe they are if someone has actually seen Marshalls with the "M" suffix. I wonder how many Marshall barrels were sold?!? I apparently have seen the results of at least two! Still, it seems strange that they are otherwise in the correct serial number range. Can that be coincidence?
I disagree a bit with dfw on the value of the Blue Book for Colt information or values. For example, the Blue Book has introduced "issue" nomenclature to Colts, which may be fine for convenience, but the way it defines the various "issues" is not correct in my view. (For instance, it lumps all Pre-War Detective Specials as "First Issue." What about the square butt from 1927 to 1933? Would not that be "First Issue," since the round butt ("Second Issue?") then continued to early Post-War? I see the major variations as the initial square butt long frame, the round butt long frame with half-moon front sight from 1933 to 1947, the long-frame with ramped front sight blade from 1947 to 1966, the short frame unshrouded ejector rod barrel from 1966 to 1972, the shrouded ejector rod barrel from 1972 to 1986, the reintroduced DS from 1993 to 1995, the DSII, the SF-IV, etc.. Would the 1950s "Coltwood" plastic stocks era be another issue? (It would be to me.) The Blue Book mentions only three issues, but, by my count, there are many more. To me, it is a worthless concept if it does not deal with the major variations like frame shape and length, sight style, etc..)
As far as BB values being accurate, I doubt that any NIB Marshall's can be bought for the $875 BB price. Well-worn Marshalls probably would bring that. However, the BB is still often a valuable reference for relative values and general information. Just do not rely on it as correct in all cases, with Marshall values being one. Military automatics are another. Pre-War National Matches are another, etc..