Johnf - I remember that interview, now that you mention it. I trust pretty much everything Bamforth says about brewing.
I was wrong about the protein rest. I double-checked New Brewing Lager and Noonan says to never use a stepped mash with British or Brewer's malts, because the low-temp rests would effectively "over-modify" the malt.
For lager malts, Noonan gives 30-33% SNR is undermodified, 37-40% is overmodified. For ale malt 38-42% is the sweet spot, while 50% is too much. He does say if the malt is over the recommended range, brewers should shorten the length of steps, or increase the temp of steps. If the malt is under the desired range, you should lower the sacc. rest length or temperature, and add or lengthen a protein rest.
In some of the commercial recipes I've seen, I've noticed higher-than-usual sacc. temps, like 160-162* so maybe this is why.
To get back to PawPat's original question, maybe we should think about what the Kolbach is measuring. Total nitrogen affects yield, clarity, and head retention. 30-40% of nitrogen in malt will become "permanently soluble" during the mash and I assume the rest will precipitate out during the boil and chill. Half of the soluble nitrogen is formed during malting, the other half during proteolysis during mashing. At 50%+ SNR the beer will lack body, and over 12% total protein the beer may cause haze problems.
So in PawPat's example, I would guess it's more likely that the low SNR will be a bigger problem than a low total amount of protein, but I'm still thinking about this and may come up with more later.