A follower of my LinkedIn page asked this Microsoft licensing question:
"A customer had 672 Office Professional Plus licenses with active Software Assurance until September last year. Then they bought 608 M365 E3 From SA subscriptions in October.
"1. Do they retain all 672 perpetual licenses along with the 608 M365 E3 from SA subscriptions?
"2. Do they only retain 64 out of 672 perpetual licenses, and the rest are superseded by 608 M365 E3 From SA subscriptions?"
My answer: They retain full rights to use all of the 672 perpetual licenses. "From SA" subscriptions do not supersede their qualifying perpetual licenses.
Note: Since SA on those perpetual licences has expired, Software Assurance benefits and rights granted through SA have also expired. They only retain the rights of the perpetual license.
Disclaimer: This is an informed expert opinion. Always clarify terms in writing with an official representative of Microsoft.