cerealkiller,
I think it might be a good idea to talk to the operator you are going to fly for. You only need differences training to fly an NG, the test you have done should be acceptable for 300/400/500. There isn't even a difference in the pressurisation / airconditioning panel between the 300/500, just on the 400 which has an extra cabin zone in the airconditioning and an extra knob.
The same thing happened to me in reverse, when the type rating was issued by the CAA it said 737 300 series, to fly a 500 there was no differences training / testing. At my next IR renewal the TRE signed it as 737 300 - 900 series. This was with a UK operator that didn't even fly NGs, just 300 and 500.
I think the CAA may have got their wires crossed a bit.