I agree with you (and prior versions) that you should be able to enter "various" as the sale date, enter the summary proceeds and summary cost, and just attach the PDF. Setting the sale date to 12/31/20 is technically incorrect unless the sale date was actually 12/31/20.  I don't know if the IRS is going to have a hissy fit if practitioners set the date to 12/31, but it is sure less of a time waster than entering 6 pages of stock transactions simply because (in my case) TP has $8 of disallowed wash sale losses that preclude me from entering "D" transactions in the summary line of the 1099-B worksheet.

I suppose another option is to leave it blank, run the error checking before e-filing to confirm that this is the only error, then disable error checking before e-filing.  Leaving it blank is no worse than setting an incorrect date, IMO.