OK, I think I understand the question:  Does "first tax year" mean first calendar year, or first return filed?  In other words, can the 2019 and 2020 amended returns be filed after the 2021 return, which need to be filed in order to get the ITIN through the W-7 process?  I think the statute and regulations are clear that the rule applies to the first tax year, regardless of the order in which the returns, or amended returns, are received.

I would file the amended returns now, with "Applied For" as the spouse SSN/ITIN.  At least that corrects the illegal use of Single filing status.  It also may start the interest computation date for the refund.  IRS may send the return back or, more likely, send a notice asking for the ITIN.  By that time you should have it.  "Service" is part of their name, not the taxpayer's.