Non-reporting servers following AV replacement

I recently completed a push of 12.1.4 to over 1k servers.  This was to replace McAfee.  While looking to see who needed to be contacted to reboot their servers I've uncovered almost 500 servers not reporting to the SEPM.  All pushes completed successfully however when testing a small batch of these servers the SEPM is only seeing McAfee EPO on them.  Is it not going to recognize that SEP is installed until after the reboot and thus this is a good indeication of who needs to reboot their servers or did half of these replacements actually fail?