David, I hate to disagree with you but I think all of the Luminars but the 16/2.5 are triplets.

I have 25/3.5, 40/4.5, 63/4.5 and had a 100/6.3. Triplets all.

I had a 16/2.5 that appeared to have been cooked in an oven, the balsam had run out from between the two cemented elements to form a crust around the periphery of the first element. I have somewhere, probably can't find easily, drawings of cross-sections of all of 'em; they show the 16/2.5 as essentially a tessar with a field flattener, the others as triplets.

For those watching this discussion, we're deep into lens trivia that has no practical implications at all.

Cheers,

Dan