Validity of an Type Rating
If renewed no greater than 3 month before the expiry date of the rating the rating is valid to the date of the previous expiry date + 12 months. (ie the anniversary of the original date).
You are correct the guy who did your rating incorrect. He was probably confusing the UK rule that allows the rating to be valid to the end of the month in which the test was conducted as long as the pilot is employed in an AOC company and the test is being conducted by that same company. (A CAA sop to BA when JAR FCL's came in.) If not it is to the actual date, in your case some time in March. If you cannot get the guy to change your licence entry get any TRE to do it.