I have 11 different notched, no advertising on back.

I had 2 or 3 of most of the 11 at one time. Traded the spares.
I got mine from a Chipco salesman.
If all 3 salesmen got several sets, that does not account for the amount of these I've seen.
I have a couple not notched, with table wear.

I always figured Chipco made 20 of each notched as samples for the Mirage. If so, how did most of them get out?

BTW, I think you are offering them a fair price.