Maybe it was too big an assumption – there are lots of pairs XY with both elements coming from the bottom row. Unless this is a very unusual text there are far too many to get from digits in the plaintext, but that makes me think. Maybe this is not quite the standard Playfair cipher? Maybe, the pair shift rules are different from the usual ones? The question is, what are they?
A pair XY where both are in the same row -> ?
A pair XY where both are in the same column -> ?