Brian,
Yes, success!
That's a handy pdf file you have. I found a DVD copy of Westerfield's for $99, which is a wee bit over my current budget.
I agree with Bruce that it "Might be American Smelting & Refining, a company with Mexican connections" as he has stated.
Several of the Barringer photos of 16 car, Lot 8687 show two different reporting marks,
M.T. y A. and Veta Grande. There was a Lot 8687-A and a Lot 8687-B.
Also, the various Barringer photos I've recently located, are of the same design ore cars, and possibly all destined for the same company, ASARCO, to be delivered to the two Mexican mining companies.
I ask a big favor...
May I possibly impose on you to provide the same "Lot Number" information for the below 3 lot numbers for the other ore cars?
Lot 9102 - Veta Grande ore car no. 107, with a build date of 12-20
Lot 9221 - M.T.y A. ore car no. 213, with a build date of 11-21
Lot 9388 - M.T.y A. ore car no. 214, with a build date of 10-22
Thank you.
Al Clemens