How is it possible for a person to enter into the military twice, even if it is in the early days.
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Are both periods of service under the same name?

One scenario is that they were too young to be in the military, released, and then joined again when they came of age.

Another is that they served their time, were discharged and then enlisted again at a later date.

Could one period of service be as an enlisted person and the 2nd period as an officer?

I'm sure there are more reasons, but these are a few.

Art Thomas