You might want to talk to Martin Meyerhoff in Germany. You can find him on the Slack channel for the Solidus project.
I know for a fact that Spree versions below 2.4 have severe problems with VAT calculations, and been led to believe that the calculations are so wrong that using those broken versions of Spree may be illegal in some EU countries.
I don't know what work has been put int into the VAT system in Spree 3.0, 3.1 and so on, but I do know a significant amount of work has been put into this in Solidus to make the platform compliant with VAT-requiring countries.
Fixing the broken VAT system from a Spree 2.2 installation is not a trivial undertaking.
-Jason