Like Gene said the chips are ordered by the casinos and the casino can cancel the Win Card Promotion at any given time (and in a couple of cases never even run the promotion).

I know that there are a couple casinos (Lady Luck and Boomtown in Verdi) that didn't use a Win Card Branded Chip.

The Trop chips could have been from another promotion and they just used the chips and never ran the other promotion.