There are a number of things going on here. One is the fact that companies will often not report all the details of their technical specs, perhaps out of a desire to make their spec sheets more neat and tidy but more likely to "fudge" on the answers to make their products look better. So if there are no details given, assume they're using the "worst" number than any other equivalent spec.
In the case of mics or anything else involving decibels, there's often an "A" weighting that attempts to compensate for average sound perceived by the human ear for general program material (there's also a "C" weighting for music-only material, I think, but remember it's 5 in the morning).
When I was previously researching the question about the noise of the SM57, I also picked up the Beta Green 5.1 spec sheet. That one says 21 dB noise (A weighting) and 25 dB (DIN 45 405 weighting). 2 numbers here too, but at least they tell you what they mean...but no S/N ratio listed! What to do?
Well, the S/N ratio isn't actually a ratio. What it is is the difference between the noise floor (internal noise) and the average SPL (sound pressure level). Shure lists the average SPL as 111 dB for phantom power with A weighting, so the S/N here would be properly listed as 90 dB(A).
