Katharina,
in our country, we normally get (if we buy it from an official Laser merchandizer in HH, B, DU or Überlingen) our new sails from the Laser-manufacturer in the UK. This means for you (and also me) in likelihood 99,9% it is a Hyde. That´s also a reason, why it is so expensive for us here, to get a new sail.
For your question about "Mk5" / "Mk6", read the text at the following link, that is placed at the ILCA-Webside and tells a bit about the reasons for the change from "Mk5" / "Mk6": http://www.laserinternational.org/rules/lrsail01.htm