Generally, they need to be scanned again. First step is finding where they are, which can be a royal pain given where they’ve been installed over the years. Just going by the installation scripts, they could have been under the BFD, BFD1, BFD3 directories, in expansion pack directories, your user FXpansion directory.
If you still have v3.3 installed, you can look at your Content Locations, and it will show you everything. If not, you’ll have to do some sleuthing. Generally you’re going to be searching for files with bfd in the name somewhere.
Take this as an opportunity to move them into one place where you can find them again. My personal preference is to keep expansion pack grooves with the expansion pack itself, or to treat a bundle of grooves (say, Groove Monkee), as if it were a single expansion pack.