I think it's safe to assume that he meant 1990 was the transition when they started producing .170. Which means that .155 and .170 were made. I'm sure they didn't stop making .155 on January 1st
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If you want to pick nits-
The most correct statement is Colt transitioned to the .170" holes in 1990 and used them until 2008.
For further correctness, it needs to be determined what year Colt transitioned back to the small hole- 2007 or 2008.
Did Colt make large hole receivers for the military? If not, then Colt did not use the large hole receiver regardless of customer