Is my previous form still good?
The current medical form is essentially identical to the forms that were used in 2014 and earlier. However, the current procedure requires a doctor to sign off on you being "good to race". As the old forms required were only a self certification of readiness, they do no carry over to 2015.
This policy matches up with all the major racing organizations (NASA, SCCA, PCA, et cetera) and additionally, a medical exam is required in order to receive an FIA rally license. Fortunately NRS has worked it out so that your NRS medical form will be accepted when applying for your FIA license.