The "A4" is for textile manufacturing, the "99" is the Hersteller (maker) permit number that was granted by the RZM, the large "A" is a cost code, and the six digit stamped number is the production number. More information on H.J. RZM tags can be found in the "Handbook of the Hitlerjugend" by Wim Saris on Bender Publishing. Also see this thread.