In order for the published figure to have any meaning, it must include the measurement bandwidth, including any weighting filters and the reference signal level. Stating that a unit has a "S/N = 90 dB" is meaningless without knowing what the signal level is, and over what bandwidth the noise was measured. For example if one product references S/N to their maximum output level of, say, +20 dBu, and another product has the same stated 90 dB S/N, but their reference level is + 4 dBu, then the second product is, in fact, 16 dB quieter. Likewise, you cannot accurately compare numbers if one unit is measured over a BW of 80 kHz and another uses 20 kHz, or if one is measured flat and the other uses A-weighting. By far however, the most common problem is not stating any conditions.

Correct: S/N = 90 dB re +4 dBu, 22 kHz BW, unity gain

Wrong: S/N = 90 dB