The Play Data microapp (when Data Playback Type = Number) uses the sys files supplied by Cisco. There is a "hundred.wav" file and a "1.wav" file so I guess CVP is analyzing the number then making up a VXML page with the WAV files it wants to play. Obviously you have re-recorded your versions of these files, but the logic that makes it want to play 1.wav, hundred.wav, and.wav, 23.wav is hard coded.
I don't think this can be changed.
An expensive alternative is TTS.
Regards,
Geoff