It reads to me that your engines starter does not crank the engine at all when you're trying to start the car right(not cranks but fails to start)? If so, I don't know why either dealer would look for codes in Vadis as there simply wouldn't be any for that condition. It also has nothing to do with the "lawnmower syndrom" (below).
It being a complaint written up and recorded previously while under warranty, it should still be an issue covered and ANY Volvo dealer anywhere should be able to deal with that regardless of where the car was purchased as records can be forwarded.
If you're getting a runaround from both dealers now while still not fixing the problem, you'll need to call Volvos customer service # and they should be able to persuade one or the other to do whatever's necessary to properly diagnose and repair the car.
Now, a "no crank" condition should be first duplicated by the tech, then he needs to fault trace to see which component isn't passing current assuming that there's no voltage at the starter itself. If they're unable to duplicate it (like it starts everytime at either dealer), then all they can do is guess and it's easy to guess wrong. It could be a faulty connection, faulty starter solenoid, relay (already replaced), "PNP" or gear position switch (typically older 850 problem) or ignition switch. There's alot of room for incorrect guessing IF it can't be duplicated at any dealer.