Originally Posted by JohnBurke

Bruce Chien is an excellent source. He's well recognized and well respected.

Your first class medical does NOT become a second class medical. It does not become a third class medical, either. A first class medical certificate, as issued, remains a first class medical certificate, no matter how long it has been since issuance.

After the six months after the month of issuance has elapsed, it is no longer good for first class privileges, but it remains a first class medical. Class of medical is not synonymous with privilege. The class of medical doesn't change. The privilege for which it is good does.

A medical certificate is never deferred simply because it has expired. If the medical has expired for the level of privilege you seek, simply go take the exam for another, before you intend to use those privileges.

You do not need a first class medical certificate unless you are seeking to exercise the privileges of the ATP pilot certificate. If you hold an ATP but are not involved in flying that requires the ATP (ie, flying in circumstances that only require a private or commercial), you may fly with a lapsed first class, and use it for second class privileges within the allotted time frame. Or you can simply go get a second or third class, as appropriate.

If at some future time you elect to seek a first class medical again, go get it. done.

If you have medical concerns for which your medical certification was deferred or delayed, then that's another matter entirely.