What year did they switch to the small mounting hole.  I have someone telling me they have a pre-ban large hole colt upper made in the late 90's for sale.    

If it was made in the late '90's, it is not a preban.  The AWB was signed into law in 9/94.

Upper receivers with pre ban features are still being made to this day and have been since the AWB of 1994. There is no law against making them. As long as they are placed on a pre ban lower, it is perfectly legal.

Ok thanks. I was aware of prebans still being made.  I thought the large hole was not.  Thanks for information!

I was just testifying to the fact that pre bans are still being made, not that this upper in particular was made in the late 90's. In fact, I would think it not probable due to it being a large hole. Most of the large holes were made up through the early 90's, if then. But then again, it is a Colt and Colt makes different size pins with no rhyme or reason to it. Still, I doubt it was made much later than 92 or 93, but that is just a guess.