@MauriceB’s post further up suggests things are not quite so simple, or are multifaceted.
That is an important piece of information, especially considering that - if I understand correctly, that legacy data is still there even if DTTG2 has been deleted; DTTG3 deletes it sometime down the road (where on Earth did I read that? But I did…! Here; @eboehnisch I’m sure you will have thought of this long before I did, but is it possible to preserve that legacy data for the time being? I’m kind of assuming it might be possible to retrieve “lost” data from that source, even if DTTG2 has been uninstalled? Would DTTG2 “see” the data again, if it were reinstalled?)