Such as, "Marriages that predate the effective date of this policy or entered into prior to March 1, 2000".
Another exception is if the two were already in such a relationship, then their status changed. Example being they're both enlisted then one becomes an officer.
And those who give a correct answer usually get TD'd for some reason. Linked below is the official US Army policy on the matter, which I assume is what you're interested in given your name.... It quotes the following as being PROHIBITED between officers and enlisted personnel.
Violations of the policy may be punishable under the UCMJ, as violations of a lawful general regulation. Officer-Enlisted Personal Relationships Officer-enlisted dating, sharing of living quarters (other than due to operational necessity), and engagement in intimate or sexual relationships is prohibited.Examples of fraternization include going to one another’s private homes or to clubs together, dating, sexual activities or any kind of favoritism.The senior ranking officer in such situations is considered to have greater ability to promptly discontinue any behaviors in breach of policy, but both soldiers are considered equally accountable.That is IF the relationship exists outside of the military it's OK. But if you met through your military duties, even in the Reserves, it's prohibited. This fraternization policy would not apply amongst enlisted personnel, or amongst officers of different rank, unless they were in the same chain of command.So if you were to meet someone and you both happen to be in the Guard but one is officer and one enlisted it's OK.