Missing Alkan opus numbers

[lisztrachmaninovfan]

Why is it that every list of Alkan works have so many opus numbers not filled in with works? Did Alkan never compose any works under the empty opus numbers, or are the works assigned to those opus numbers all lost?

Also, did anyone hear of Alkan's Largo al factotum, air du Barbier de Séville arrangé en rondo brillant for cello and piano, Op.5, or his Allelujah for piano in F major, Op.14? Do they still exist today? There are no signs that they do, and the last time the Allelujah, Op.14 was even mentioned in literature was in 1940.