In my specific case, I've started copying the previous last-read dates to #admintags, as 'read:2020-04-16'.
Here's the template I used to make the list:
Code:
program:
most_recent= format_date($$#lastread, 'yyyy-MM-dd');
old_dates= list_re($#admintags, ',', 'read:', ' ');
date_list= list_sort(list_union(most_recent, old_dates, ','), 0, ',')
Unfortunately, short of editing the read: tag entries I'm not sure if it's possible to do it while building the list.
Additionally: is using list_re to replace 'read:' with a space the proper method?