The basic go no go test as described is fine. However if you want to accurately determine the crystal parameters you will need more work. For HF crystals a good test jig to avoid strays is useful. Also at resonance the crystal is a series tuned circuit with very very low loss resistance R. This is not a good match to the nano vna which is 50 ohms. There will be both phase and frequency shifts as well. Unraveling all these for the crystal parameters is a challenge.
F4WCV