nevermind, i finally fixed it... after trying a billion things.
the end of each song needs to have:
_root._global.songnum = x;
where x is the number i want to assign to songnum.
christ... i tried every possible thing, but never tried _root 'cause i assumed once you make something _global you can address it from anywhere with just _global.varname
oh well... what a relief! hours and hours of ARGHGHGHG.