My MTHFR gene mutation test says 'not detected' but the note below it says 'this assay detects the mutation C677T in MTHFR'. Does it mean I have it?

MTHFR mutations. MTHFR is the gene which produces methylenetetrahydrofolate reductase. Over 50 known mutations in this gene cause reduced function of the enzyme. The most common mutation causing homocystinuria is the C677T mutation, which among other problems increases the risk of stroke. I can't tell how many mutations your particular test could detect, but you do not have the C677T mutation.