The leaves are the best clue. Paph. lawrenceanum has narrower leaves with a "clothlike" texture. Paph. callosum tends to a wider leaf, but more importantly a waxy surface. Most Maudiae's are intermediate in texture. Look closely at and fell the surface of both species, and then a Maudiae, and you should be able to get a pretty good idea of sorting them out.
I was worried it may turn into a comparison of in hand stock.
Anything consistent about petal warts? Lawrenceanum has warts on the upper and lower margin of the petals and callosum only has warts on the upper margin. The callosum petals are also downswept versus almost straight out in lawrenceanum.
The alba Maudeae pics I've seen have petals like callosum, somewhat downswept and warts on only the upper margin (although the colored forms seem to go both ways).