Not always as it sometimes doesnt mix at all...get the water checked for gas (i forgot ther name of the machine they use) but basically they check for exhaust gasses/carbon coming thru your water via header tank/filler neck that will be a dead cert to see if head has gone...
As has been said dont be pulling the head til you have checked the turbo....
Maybe an oil feed to it...
and again what colour was the smoke was it cloudy or was it blue or blue?
When i rang i got told the k's when it was 1st registered and when the previous owner had it, i then gave them the new k's...
So yeah you should find out
Glad its all sorted the could of been really arses and said not our fault blah blah blah
Its always nice to hear when garages make good of somthing they did wrong with little hassle...