No, i just checked again. Nothing on the left rear tube. Aside from the 'prelude' logo, the only other thing which may help put this puzzle together is a sticker on the seat-tube at the very bottom:

it says TRE TUBI RINFORZATI, then under it it has picture of a dove with 'CHROMO MOLIBDENO' adjacent to it. It also has 'TENAX' under it, and 'COLUMBUS' under that...