[CentOS] md boot device

The secondary disc was used in a lab rig to boot off of and test something
after which the primary was replaced and the system was booted off of. It
saw the secondary as more recent and dropped the primary so, the secondary was
removed and the primary was used to boot.

Figuring that made it more recent, even after it was restarted with the "now
older" secondary, it still wants to drop the primary?

W/o blowing out the secondary (it can't be hot added) how can I force the
primary to not be dropped? I'm amused that even with it used to boot solo,
and hence timestamps validating it as most recent, md will only use the
secondary to start from?

Thanks!
jlc