Jekyll Paginate V2 and (maybe) generating front matter

Trying to fix a Jekyll Paginate V2 date/time sorting problem, possibly by processing/injecting/generating additional front matter.

I have a blog with “regular” and “event” posts. The event posts have a startDate that the regular posts do not, but I would like to sort them all together in one list. Using Paginate V2 (locked to 2.0.0 because of the makedir error. When I set sort_field: 'startDate' it processes, but sorts pseudorandomly. When I set sort_field: 'startDate:date', same thing. When I set sort_field: 'date:startDate' i get

jekyll 3.8.5 | Error:  undefined method `has_key?' for 2010-06-23 00:00:00 -0700:Time

which is apparently a Jekyll problem of sorting dates with time stamps (and maybe related to the sort_field: 'startDate' not really working?)

Manually adding startDates to my non-event posts did not solve the improper sorting whether it’s a Jekyll proper or Paginate V2 problem (I just rechecked the Releases page and I am using the most current Jekyll short of pre-Alpha stuff).

I don’t, however, want to remove the times from my startDate stamps because they are needed elsewhere.

So, can I generate another front matter field for Paginate V2 to sort on? Even better, can I also give my non-event posts this justDate field through non-manual means?