There are at least 3 variations of the C/X C/X C/X acceptance marked Lugers that were routed from commercial production to military use during the build up in armament during late 1913 to early 1914.
The first variant is what might be called a “1908 Commercial/Military”. It is a 1908 pattern
without stock lug completely constructed, finished, numbered in the commercial 5-digit fashion (in the approximate serial number range 69000-70100 that you noted) and
bearing no chamber date, evidently still in the inventory but without final commercial proof before being diverted to the military and acquiring acceptance and proof marking (I have #69879).
The second variation is what I call a “1908/14 Military/Commercial” (note the commercial/military description reversal
). It is of the 1908 pattern
without stock lug, evidently still in the stock inventory but in unfinished condition since it is numbered in a 4-digit a-suffix military fashion (in the approximate 8000a-9400a range as noted by Jan Still). Apparently, it received final assembly, finish, numbering, acceptance/proofing and a
1914 chamber date when transferred to the military (I have #8310a).
The third variation marks the transfer of last of the pre-war commercials to the military, produced late 1913 early 1914,
bearing no chamber date and
with a stock lug. This could be considered a “1913 Commercial/Military” (or a “1914 Commercial/Military”?). I do not know the approximate serial number range, it may start below the aforementioned 70100 but most likely just above that number (I have #70185).