Filter by merged cells in Google Sheets?

I need to filter a data table by date values. Unfortunately the date cells are merged like so:

So if I would write

=FILTER(B1:B; A1 >= DATE(2020, 4, 1))

I only get every other value in Column B. I guess I should combine two filters, one of which has the source offset by one, but then I'd get a range mismatch error, because the source range would be one row shorter than the one in the condition statement.