Without rehashing the whole discussion, I suggest:

1. "date accessed" is not a good name, because as we've seen it has a number
of connotations.  I suggest 'dateLastValidated' which is what Rebecca had in
mind originally, to mean the last time that someone (with the authority to
do so) said that the item was up-to-date.

2. "Date valid" is not a good name, because similarly, it has a number of
connotations.  I suggest 'dateApplicable', to mean the date that the
information contained in the item will become (or became) valid, like a
train schedule.

3. If "date of last access" is needed, call it 'dateLastAccessed'.  However
I'm not suggesting we add it.

There's also been discussion of urls and how they fit with this ....  I
don't think it's been sufficiently thought out. I'll post my thoughts  in
another message.
--Ray