probably my vision is a bit naïve (and I'm ignoring all this
philosophical and linguistic examinations :-) ), but isn't only a
problem of label and display?
If so, I think that is a good idea to make encoding as simple as
possible (but not simpler :-) ).
In this way, I would prefer unittitle and unitdate divided, because
mixed content it's often (always) a mess.
Then in visualization, if there is no unittitle, you could choose to
use unitdate (even if dates aren't in title) as label and so on.
Just my 2c (of euros)