One needs always to follow-up positive *screening* with *confirmatory* testing by gas chromatography-mass spectroscopy, or GCMS, which gives a molecular fingerprint for the substance present.

With the GCMS test they will be able to tell what benzos are in your system for sure. So even if you protest and make them retest, you are still screwed. Even though they are wrong to give you a negative without a CGMS test because all the urine benzo tests just show a positive for benzo, not which one. They are lying or stupid, simple as that. Your best bet is to call their bluff and see if they will do a CGMS if they say yes then you will test positive unless its after the 3-12 days since your last use. If they wont do the CGMS then you have a right to sue them and demand your job.

Drug Urinary Metabolite Detection Time with the CGMS
Alprazolam (Xanax) hydroxyalprazolam 1-3 days
Bromazepam (Lectopam) hydroxybromazepam 1-3 days
Nordiazepam (Clorazepate,Tranxene) oxazepam 3-12 days
Chlordiazepoxide (Librium) oxazepam 3-12 days
Clonazepam (Klonopin, Clonopin) aminoclonazepam 3-8 days
Diazepam (Valium) oxazepam 3-12 days
Estazolam (Prosom) hydroxyestazolam 2-5 days
Flunitrazepam (Rohypnol, Roofies) aminoflunitrazepam 1-2
Flurazepam (Dalmane) hydroxyethylfluazepam 2-4 days
Lorazepam (Ativan) lorazepam 3-7 days
Medazepam (Nobrium) oxazepam 3-8 days
Midazolam (Versed) hydroxymidazolam 1-3 days
Nitrazepam (Mogadon) aminonitrazepam 3-7 days
Oxazepam (Serax) oxazepam 1-3 days
Prazepam (Centrax) oxazepam 3-12 days
Quazepam (Doral) noroxoquazepam 2-4 days
Temazepam (Restoril) oxazepam 1-3 days
Triazolam (Halcion) hydroxytriazolam 1-3 days