Bush was AWOL.
Why you're right:
1. Bush did not complete the required 48 drill units in fiscal year 1973, as required by law. (At the time, the fiscal year lasted from July 1 to June 30 of the next year.) Payroll records released by the White House show Bush only completed 36 drill units during fiscal year 1973. According to Lawrence J. Korb, Assistant Secretary of Defense for Manpower, Reserve Affairs, Installations and Logistics under Ronald Reagan from 1981-1985, that proves that Bush was AWOL because “If you don’t show up, you’re absent without leave, by definition.” (13 U.S.C. 502; GLCQ; Blue Lemur)
2. Bush didn't make up that training within the required time period. According to Air Force policy all “substitute training” had to be performed “within 15 days immediately before or 30 days immediately after the regularly scheduled” training. Bush did not perform any substitute training 15 days before or 30 days after his missed drills in fiscal year 1973. And "transferring credits from year to year is in violation of military law." (Army Field Manual; GLCQ; Blue Lemur)
3. Bush did not receive special permission to miss his training or make it up at a later time. The Bush campaign does not claim he had special permission and has not provided any evidence that Bush made up the time at a later date. (Blue Lemur)
Why they're wrong:
Bush told Tim Russert, "I did report; otherwise, I wouldn’t have been honorably discharged.” But that doesn't prove that Bush served; it proves that Bush got away with it. It's like arguing that since you've never been convicted of a crime, that proves you've never done drugs.