Plus if this untrained tech WAS to misinterpret a faint line as a non-negative and sent the sample for GC/MS confirmation, wouldn't the GC/MS quantitative analysis show some detection even if below the 50ng level since they are testing below that level?
The cutoff threshold for the GC/MS is typically 15 ng/ml. But dont let this create another worry for you. Read this thread:
http://boards.cannabis.com/drug-test...d-testing.html

If the sample registers below 15 ng on the GC/MS, its ruled a negative - no quantitative value is provided because its not necessary - a negative is a negative. Above 15 ng is a positive and at that point a quantitative value is provided.