Optimized Media in Media pool list

I have a question about Optimized media in resolve 16.. I'm working on a multicam with optimized media made from UHD originals for 5 main cameras and about 30 B roll shots . In my media pool list view I have a column for optimized media and they show up for my 5 original cameras, but only about 3 of the B roll shots show optimized media and the rest say "none". On the other hand everything seems to be playing OK at least so far.

Virtually all of those B roll shots though have been turned in to subclips . In fact I think the ones that still show up in the Optimized column are the ones that don't have subclips. None of the subclips show anything in the Optimized column either.

The timelines don't show anything in the optimized media column

Its all working beautifully (so far) so i'm not complaining but i would like to to know how this all works.

I don't use Subclips, but as they're not a reference to unique file on the hard drive, I would guess they don't get Optimized. Only real clips do.

But they’re made from originals that do have optimized media so I would assume like a timeline they can continue to reference them . It’s the originals that they’re based on that no longer show that they’re optimized in the list though . Odd