The manual just says 800 but there is a page on Optional Datacards.
"Flybuddy Plus is the datacard option and is available as an upgrade for
Flybuddy pilots."

Our unit has a datacard slot in the front and there is something in it but
it may just be a cover or blank plug. Nothing that it says would be on an
optional datacard is active.

Could the data card slot be there and internal components required to read
it missing i.e., part of the upgrade referred to in the manual?

This unit does a fine job for the simple airspace we mostly fly in. I'd
like to put off a GPS purchase for a couple years but it would be nice to
have a database that doesn't predate the change in identifiers of many
airports.

Purchasing a more recent plus version for $150 and swapping it in sounds
like a good option to me, thus my original post. I guess I'll look around
on Ebay.