As the onus of taking Individual Physical Proficiency Test (IPPT) /NS FIT is with the individual, you should be able to determine whether the medical excuse for your injury will last beyond your current qualifying window and whether you have accumulated enough medical excuse to be exempted from the IPPT/NS FIT. You will need to keep records of all your medical excuses and submit to your NS Unit last month of your qualifying window to appeal against being dealt with as an "IPPT/NS FIT Defaulter".