The Left slide is rollmarked 'COLT'S MK IV/SERIES 70; COMBAT COMMANDER; 45 AUTOMATIC CALIBER', all in large print. Early in 1970 that was again changed to a prefix of SM but BATF didn't approve it so Colt changed to a new number sequence and a prefix of 70G, 70L, 70S, or a G70 suffix. Originally posted by flusher. Original MKIV/Serial 70 Colt Serial numbers started with 70GXXXXX and ended with XXXXX70G. Any idea when the change occured? According to the 23rd Blue Book '70G', '70L', '70S' prefix = 1970-1976 'G70' suffix = 1976-1980 'B70' suffix = 1979-1981 '70B' prefix. Feb 17, 2011. I'm looking at a Colt 45 auto Mark IV/Series 70 - SM35XXX I can't find any specific info on date of manufacture for these guns with Serial #'s starting with SM. I can find 70G, 70L and 70S.but nothing about SM prefix. Esxi Intel Nic Drivers on this page. My Blue Book states 'Series 70 models were serial numbered with 'SM' prefixes (approx.