For me, 'touching up' an edge generally means restoring it to a previously, well-known baseline of cutting performance. This means I've already used the knife for a while with an edge I gave it (to a full burr, the first time), and I have a clear picture in my mind of how it performed when that edge was at it's best. So, if it goes a little dull, I don't necessarily expect to re-form the burr while touching it up; or, at least forming the burr to the same degree.
I'm a strong believer that a little bit of burr is always a good thing, as it provides the proof of a full apex. But in a quick touch-up of a blade I'm already very familiar with, I'm usually just looking to see if it'll get back to a well-known benchmark for cutting, based on what I've previously known it can do. That gauge is easy in itself, as I almost always test an edge by slicing fine paper, like phonebook pages, as well as checking durability of the apex by making a few cuts in wood, for example, and then re-testing how it cuts the paper afterward. If all is done well, the edge will continue to slice easily through the paper without snagging or slipping. If it snags a bit, that's almost always evidence of the burr folding over (which obviously verifies it's there). I'll do what's needed to clean up the burr, and then recheck everything again. So, I might find a little bit of burr in touching the edge up; but, I'm not necessarily expecting to see it, if all the cutting tests pass with flying colors.
David
