Erfurt 1918/20 true double date
 

I traded my Sig Legion SAO on a Luger site unseen because I have always wanted one. it has a different frame and receiver but receiver is an Erfurt 1918/20, completed in 1920 from 1918 parts. I have only seen 2 references on this site can someone help

Welcome.
But to get any significant info, you need to post good pictures.

If it is marked 1918/20 - and not 1920 over 1918- it is just what you say you think it is; they are not rare but uncommon.

Being a mismatch likely puts it into "interesting" shooter status.

Here is a picture of the receiver on my example.