8955 DB Plan

[SSRRS]

In a DB plan audit they are asking for the 8955 for that year as 2 employees terminated in the year of the audit 

1. Technically you have until the following year to first report the new termination and vested benefit. 

2. How do you prove the 8955 was filed if it was mailed ( prior to 2024 still mailed) with regular first class mail?

A. Thru showing a copy of the signed and dated form that was mailed in?

B. And must a signed copy be located or suffices if just have a copy of the form that was mailed?

Thank you