If the individual is taking a makeup, retesting, or an APFT failure then it is my interpretation that the 8 month period does not apply and the Soldier may be tested until they pass the APFT or they fail consecutive APFTs and are separated from service.
Extract of AR 350-1
G-9m(3) Soldiers in RC TPUs will take the APFT once each calendar year. A minimum of 8 months will separate record tests with no more than 14 months between record tests. Soldiers that require makeup testing or re-testing for an APFT failure are exempt from the 8-month rule.