My PSAO tells me that it is impossible to be promoted to Sergeant from Corporal unless I have served at least three years as a substantive Corporal. I went up in September 2010, I have Signals JCLM and a MATT instructor qualification done and spent May 2011 to May 2012 attached to a regular unit. My SJARs are excellent. I am with 2 Sig Bde. Is he right?