The tank capacity is five quarts. Since the water flow to the bowl shuts off quickly after flush, I think it is 1.6 gpf.
The American Standard web site says the Veneto is 1.6 and the tank interior parts look the same as the parts diagram.
The question is whether earlier versions might have been, say, 1.8 gpf, something that's hard to eye-ball. Worst case, later today I'll put a bucket under one of the units.
I'll put in another call to Porcher.
For the record, these toilets, installed by the previous owners, have performed very well for me.
Also for the record, it's very frustrating that water conservation certification in Los Angeles depends on individual plumbers making guesses about a toilet mechanism they've never seen before. The first plumber did call American Standard, who said that the model was 1.6 gpf, but he didn't believe her.