Did you observe whether the vacuumed tables' relminmxid advance? If it
didn't, then those vacuums are a waste of time.
Note that freeze_table_age affects when vacuum does a full table scan
vs. when it skips pages due to visibility map. A vacuum that does a
partial scan does *not* advance the relfrozenxid / relminmxid; only
full-table scan vacuums can do that. (Except in 9.6.) If the
relminmxid ages are younger than your 100 million table_age, vacuum
won't do a full-table scan.
Yes they did, they all advanced, and no they are not younger than 100 million. They were all over the default value of 150 as are the remaining 2, relminxid/relfrozenid advanced, relminxid to match NextMultiXactID and age went down. But good point to keep in mind.
Best regards
Daniel