I think you're missing a few key concepts, which the manual would have cleared up, but I can point you in the right direction. I will be referring to pages of the manual where appropriate.
To start with, Windows and Crossover aren't directly related. What Windows version you ran at one point has nothing to do with the "bottles" that Crossover creates. A bottle is an isolated unit in which each software is installed on its own, preventing interference between them. The bottles "declare" themselves as a certain version of Windows, which at this point is winXP by default. This is because, believe it or not, generally winXP is still the best choice. You can choose the windows version when you install, as per the manual, in this link's section.
If your software actually requires win7 and up, you can no doubt select that as a bottle windows version.
Keep in mind that Crossover could be conceived of as a translator. It "translates" Windows type instructions into instructions for your OS. Like all translations, it is possible the translation is incorrect or incomplete. Crossover does have a large "Windows vocabulary" if you will, but it doesn't translate the totality of the "Windowsian language" (metaphors employed here, not technical terms 😀
). Hence, some stuff works, some stuff doesn't. Crossover does make the Windows software believe it's on an actual Windows PC, but there is no actual "emulation", nor is there a single bit from Windows in Crossover. That means even if winXP is now defunct, it doesn't matter, you won't be running old insecure code / OS at all.
In other words, you were on the right track. Unless your software refuses to install on a winXP version bottle, you don't even have to care.