I haven't seen any release notes for that ServicePack, but perhaps Corel will update the 'Updates' page eventually - if they still do that.
The SP2.1 updates the program to version 102B22A
The SP3.0 updates it to 102B26A. This doesn't look like much of a number change, but the updater uninstalls large chunks of the program and then reinstalls new chunks, so a lot has been replaced. The updater has about 175MB devoted to GameHD_1x, about 16MB devoted to CPDecoderpack, and about 3MB each to GameCapHD_USB x64 and x86. Given the amount changed, it might take them a time to write up the release notes
Hope this helps . . .