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@Bill50 wrote:

19a asks "Was the property not used as the taxpayer's principal residence for any period after 2008?"  It was not used as her principal residence for the period 7/1/17 to 6/30/20 so the answer to line 19a has to be "Yes."

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Apparently the "Help" doesn't list the exceptions.

If you want to answer "yes", fine.  But then Line 19b is ZERO.  Days AFTER the last time it was the Principal Residence are NOT "Nonqualified Use" days.