I know all about the different oaths. Other than your statement, where is it written, proclaimed, codified, etc. that the oath of office doesn’t expire upon termination of employment?
The oath for enlisted personnel is different and they take it each time they re enlist. Technically, the enlisted oath can’t legally be enforced once the term of enlistment expires. What the. binds a former enlisted soldier to that oath is just his honor - or lack of it.
For officers it’s traditional to repeat the oath upon promotion, but it is not required once that oath has been taken once, and it does not have an expiration date. The same tradition is true for the president, senators and congressman upon reelection.
It’s also the norm in federal service to recite the oath of office for each new position, regardless of whether you have taken the oath before. In that case it is both tradition and checking a box on the personnel form to ensure the incumbent in the position has in fact taken the oath of office, and repeating it is a lot easier, faster and more efficient than reviewing a personnel file to verify the oath was taken