FCL.025
(b) Pass standards(2) Unless otherwise determined in this Part, an applicant has successfully completed the required theoretical knowledge examination for the appropriate pilot licence or rating when he/she has passed all the required examination papers within a period of 18 months counted from the end of the calendar month when the applicant first attempted an examination.
Para (c) which lays down the 36 month validity does not specify any alternative method of calculation therefore; it is fair to conclude that validity dates are measured to the end of the relevant month.