"dpkg -l" gives you the list of installed packages (with version numbers and some other useful information). Note: redirect the output e.g. to a file, so that package names and version numbers are not truncated to fit in the terminal window. You need to do that before reflashing, otherwise I fear this is too late.

FYI, when I restored my backup, the packages were not reinstalled (I don't remember, but perhaps I had asked not to save package names in the backup).