In some jurisdictions during some time periods a couple gets a marriage license, takes it to an officiant, the ceremony is performed, and the officiant returns the license with the details of the actual marriage ceremony to the office that issued the license. It’s all filed and recorded and all is good.
The vast majority of the time, the license is returned and filed. But there may be that rare situation when a couple gets married and the license is not returned. Keep in mind that this is unusual. Typically when the license is not returned it is because the couple did not get married. In those cases, destruction of the license at some point in the process is a distinct possibility.
Remember that the details of what constituted a civil marriage record can vary from one time to another and one place to another. What your parents did in 1967 may be different from what your great-great-great-grandparents did in 1867 even if the location did not change.