Bush's missing National Guard records

The AP has a story explaining
how there should have been at least five documents produced by the National Guard when Bush blew off his flight physical in 1972:

“Documents that should have been written to explain gaps in President Bush's Texas Air National Guard service are missing from the military records released about his service in 1972 and 1973, according to regulations and outside experts.
For example, Air National Guard regulations at the time required commanders to write an investigative report for the Air Force when Bush missed his annual medical exam in 1972. The regulations also required commanders to confirm in writing that Bush received counseling after missing five months of drills.
No such records have been made public and the government told The Associated Press in response to a Freedom of Information Act lawsuit that it has released all records it can find.”
How convenient for President Bush that these documents either can’t be found or were never produced. Kevin Drum has looked at this issue
in depth and has interviewed a former National Guardsman who claims Bush’s military service records were “cleansed” before he ran for governor of Texas.

Of the five missing documents, this is the one I think is the most important:
--Records of a required investigation into why Bush lost flight status. When Bush skipped his 1972 physical, regulations required his Texas commanders to "direct an investigation as to why the individual failed to accomplish the medical examination," according to the Air Force manual at the time. An investigative report was supposed to be forwarded "with the command recommendation" to Air Force officials "for final determination."
Bush's spokesmen have said he skipped the exam because he knew he would be doing desk duty in Alabama. But Bush was required to take the physical by the end of July 1972, more than a month before he won final approval to train in Alabama.
I would like to know how common it was back then for Guardsmen to blow off their physicals and what happened in any of those other cases. It would seem like a great way to avoid service in Vietnam – Join the National Guard and then blow off you required medical exam so that you are grounded and would not be able to join your unit should they be activated for duty. The only question is how Bush was able to accomplish this without leaving any type of paper trail.