GSTR1 VS B2C amendment.

Sir. Is it right that in any month B2C can be amended once, not more than once . For example in B2C for the month of November 2020 I had made some amendment for certain certain parties amount when I am filing Feb 2021 return , now again for different party,s in the present month ie september 2021, I need to amend B2C of November 2020. But systems says it was already amended once? . I'd it so.