Of the cases heard by the Court of Appeal, I am aware of 7* convictions being upheld (of approximately 140). The figure the post office gives is around 50, but this duplicitous as includes cases not referred (usually due a death of a claimant with no party to advance the claim) and cases where the theft conviction was overturned but subsequent consequential criminality was upheld.
If you remain in doubt, I can provide the names and the case references later. (Also, those cases assume the horizon data to be worthless - these convictions remain because after examination they were determined to be convicted on non-horizon evidence)
*A non-scientific methodology was carried out by reading the cases which cite Hamilton v PO (the criminal test case overturning the first conviction. The figure might be slightly higher but not meaningfully