I just mailed my 2020 federal tax return with my NRA spouse's SSN left blank. What outcome should I expect & what course of action should I take?

I am a US citizen living in the UK with my British husband. I file my taxes as married filing separately and my husband is not required to file with the US so has no SSN or TIN. I sealed up and mailed the return before writing NRA in the space for his SSN and am not sure what to expect. Will the IRS reject the return? I have read on several tax preparation sites that there is no need to file a 1040X for clerical errors, as the IRS will just contact you by mail requesting the missing information. Would this qualify as a clerical error and will they mail an inquiry to the UK? I have also read that if the deadline for filing the return hasn’t passed, one can mail in a second, correct return and write "superseding return" across the top which will then be treated as the original return. Would it be prudent to just do the superseding return as my deadline residing outside of the US isn’t until June 15th. I’d like to get my return processed as quickly as possible and fear the delays caused by the ommission.

Thanks for guidance on this matter.