Take a look on the back of any vinyl tin and tell me if it says to undercoat with a weak contract matt. If contract matt is your final coat then fine. If it isn't - then it really isn't suitable as it leads to peeling. Contact the manufacturer.
I don't need to contact the manufacturer because I, and every other professional decorator, know it is fine. There is no issue with painting on top of contract matt other than the one in your head.
Next you'll be telling us that the Crown Matt in 10L tubs from Q&B is ideal for mistcoating.
That should be fine. Don't forget to dilute it a little to ease application (although not essential) and if there is any bare plaster, mist it first. You can use the eggshell to mist if you want, but mix a little of it with at least 20% water to do so.
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