I recently examined a box of DCCo 38 ACP. The inspection tag reads LI10 which I believe is 1912 Sept. 10. Is this too early a date for this calibre and manufacturer?

Orange - you have deciphered the code correctly. I do not know when Domiion Cartridge Company began to make the .38 A.C.P. cartirdge - it will take a better selection of catalogs than I have to pin it down, but I can tell you that it is Catalog No. 15, from January 1st, 1916.

The first serially-produced model of Colt pistol in this caliber was the Model 1900. So, the date of your box is certainly not out of order.

Would love to see a picture of the box posted on this thread. I have an early Dominion box, but have never been able to find a date code on it.
I would love to see if yours is the same box or different in details. My box has, in tiny print in the lower left corner of the top label, “The Mortimer Company,” but I think, since it is an original part of the label, that it probably is the name of the printer or the box maker. Any comments on that from any of our Canadian friends?