T790M testing inquiry - 1265314

I have a couple of questions about the T790 mutation and how different labs might test for it. My mom just had a tissue sample tested for T790 in December at Duke and then has recently had a new biopsy to have a new sample of tissue retested for the mutation. The preliminary results indicate she is negative for the mutation. Duke has called her and asked her if she still wants her additional tissue samples sent to AstraZeneca to have them tested in their lab. Is there any reason to believe that she will test positive with their lab? Was it foolish to send the remaining tissue samples to be tested for something she has already tested negative for when those samples could possibly be used for a different clinical trial? Are there such different methods in testing that could generate different outcomes such as this? A greater sensitivity in one method? We are at a crossroads and are really stuck with how to move forward. Thank you to any and/or all who are willing to respond. I greatly appreciate any information as we face the next chapter in this journey.