Lost product key of unistalled XP Home upgrade

A couple of year ago I got an upgrade to Windows XP but I never got to installed. I Kept using W98SE. I put XP cd’s away in a disc storage bin and stored XP documentation with affixed product key somewhere else. Now I decided to do the upgrade but I can locate where the XP docs and key went. The string of 25 numbers that appeared in the sticker attached to the documentacion, can it be found somewhere in the XP installation disc? I undersyand that if I had installed XP there are ways to recover key from the registry, but how would this work if XP was never installed?