Per Robert Crandal:
Does anyone have an opinion about this? Do you think
the Access approach would have smaller yearly data files?
Is one approach more efficient than the other?

Beyond a certain point, Excel spreadsheets get out of hand IMHO. As you
noted, hidden code is one downside.

OTOH, you have the spreadsheets in place and they're working. Developing
an Access app to replace them is going to take man hours.

OTOOH, the searching for historical data sounds like a minor nightmare
to me.

Personally, I'd do it if I could.

Single Access back end on a file server (or an SQL database), distribute
the Access front end to each user's PC.

If somebody wants the data in spreadsheet format, write Access VBA to
create a spreadsheet on demand.
--
Pete Cresswell