I had recently sent a bat back to GM after the shoulder cracked continuously in the same place after a refurb by them. Before receiving the new one (which was given to my old man for christmas this year) I spoke to one of the members up there who had informed me that the GM NOW process has, more recently been perfected to the stage that you can just walk straight into a game with it. As said before its due to the extra rolling and boning they do prior to the finishing couple of bits on the bat.
I took said bat, straight in with the multitude of bat breaking slazengers and some league balls at uni and there wasn't a seam indentation in sight!
couple of cherries and that was it! The good thing about GM is that if there is an issue that arrises with the bat, contacting them directly always seems to get any issue resolved so if worst comes to worst a nice shiny new players edition would be heading your way.
I reckon just get stuck in if you have already done a load of extra knocking in in addition to the original work they had done.