Players of different instruments often have their particular charts written in such a way that the basic key of their instrument is written in one key but actually plays in a different key. So a piece for the alto sax, for example, might be written on the staff as C, but actually plays in Eb. The guitar itself uses transposition, with there being an octave difference between what's written on the treble clef and what actually sounds (an octave lower). So, when arranging a piece for a mixed band, the arranger has the choice of writing all the arrangements in concert pitch, or writing them in the transposed equivalent for each particular instrument - a tone difference for a Bb tenor sax, 3 semitone difference for an Eb alto sax, etc. Sounds complicated, but the individual musicians would have learned to read music in its transposed form.

The C Melody sax, I believe, was in the alto sax range but pitched in C, rather than the more usual Eb.

I'm sure other 'Catters can probably explain this better than me!