tl;dr: Given the specific wording "first tax year", should the W-7 be filed with: a) the amended 2019 return; b) the original 2021 return; c) the amended 2019, amended 2020, and original 2021 returns mailed simultaneously together; or d) none of the above?  Relatedly, does filing the W-7 with the 2021 return implicitly preclude amending 2019 and 2020?

Fact pattern:

• According to Pub. 519, to make the election to treat a nonresident spouse as a resident, you must "[a]ttach a statement, signed by both spouses, to your joint return for the first tax year [emphasis added] for which the choice applies." Source: https://www.irs.gov/publications/p519#en_US_2021_publink1000222193
• Client intention to file W-7 with 2021 return (currently on extension).
• Client has been married since 2019.
• Spouse has never entered U.S (married on foreign soil).
• Spouse had no 2021 income (need to verify 2019 & 2020).
• Prior returns were filed as single.
• Client would like to amend previous returns for accuracy and for MFJ tax benefit.
• Client is aware of downstream implications regarding election, and necessity of election statement.
• Spouse has not filed with SSA for SSN.

My advance thanks to the community!