Ave Edwin, you're right.
I forgot Ponsin with Second Method to Palm a Card, page 44. (1853)
His explanations are not very clear but you retains the bottom card with your left little finger as you take the deck with your right hand "ala Biddle".
Stanyon's explanations are better, especially the end when he wrote : "If the left hand be now held in the correct position althought a portion of the card projects over the little finger side, there is no fear of the card being discovered."
it's also for that I wrote that "Latapie's palm" is not really a gambler's palm as it is a FULL palm. There is no projection of a portion of the card.
The Third Method explained by Robert-Houdin, page 179 (1868) is pratically the same as Ponsin, except you take the deck by its upper side. Again it's the little finger which retains the card (as if you are going to do the pass) but R-H explains that the left thumb must also conceal the top of the upper side of the card palmed.
The two methods must be done stand-up as you let the left arm drop along the body.
May be it's for that R-H explains this palm in Secrets of Conjuring and Magic and not in Card Sharping Exposed where gamblers are generally sit down.
Ouf! I hope my english is enough understandable.