Here are our current standards (they may evolve further as we gain experience) for documenting conventions affected by Covid-19.
Document Announced Conventions
If a convention was announced and then had to be cancelled or moved, we want to document the original date/site/guests/whatever as well as what actually happens.
The documentation in an individual convention page (e.g., Boskone 58) should focus on describing what actually happened. E.g., the convention was announced for date & location with guests. In May 2020 it was cancelled/postponed/whatever and is now scheduled for date & location with the same guests in 2021. Or, perhaps, it was held virtually. Or whatever.
The documentation on a convention series page (e.g., Boskone) is more tightly formatted. If a convention is moved or cancelled leave a row for the cancelled convention and use cross-out to cross out the date and location. E.g.,
July 4-6, 2020 which is input as <s>July 4-6, 2020</s>. Likewise, cross out the venue.
If it stays with the same dates but goes virtual, leave the date uncrossed-out, but cross out the venue previously-announced and add (virtual).
If a convention is run virtually without even having had an announced physical venue, list the venue as (virtual).
Follow the Convention's Descriptions
...at least as long as it makes sense.
So if a convention re-uses a convention number (which seems to be the usual decision), then the series table should have two rows, one with the crossed out date and venue and the next with the new date and venue.
Tag the individual con page (not the series) with the Covid-19 category and list the con on the Covid-19 page.