This opus number assignment feels spurious to me for a number of reasons:
- Probably the origin of opus "29A" comes from Instytut Fryderyka Chopina; so far I failed to come up with any other website, album or catalog where this number is used.
- Even the published scores linked in above page don't contain opus info at all. For most of Chopin's other works (Mazurkas, Nocturnes etc), opus number is present in publisher info; but not this one.
- Given the nature of this piece (as a variation of another work), it is extremely unlikely Chopin would have assigned an opus to it; and I failed to find any historical info that indicates such assignment.