Missing data

A couple of years ago I recorded some data to a CD, then I recorded
some more data to the CD. When I checked the first session had
disappeared. I know it's there because the space available says it's
there but it can't be seen.

It's not desperately important data but it irritates me to lose
something. Is there any software around that could see everything on
a CD that had been written to it?

Yesterday I bought "Isobuster" and I'm hoping that might help but I
need a little time to master it.

Colin