Simple concept indeed -- but you seem to have missed it. The "precise corrective adjustment" with respect to using a dial indicator consists of turning the elevating screws while watching the dial indicator. It doesn't matter how many turns it takes.
Well, we don't see it the same way at all. I'd say quite the opposite: if you think it's *not* significantly different, there's no help for you.
Explain that one, please: if all three knives are "perfectly level to the outfeed", what is the source of error?
.. then the knives aren't "perfectly level to the outfeed" .
Trial and error...
.. then the knives aren't "perfectly level to the outfeed" .
Trial and error again.
Or you could use a dial indicator, or a straightedge and feeler gauges, to set the height precisely -- and eliminate the trial and error steps you've just described.
If that works for you, fine. I've done it that way, and I find it to be a PITA. I find it a lot simpler to use a dial indicator: pick one knife, any knife, and set it so it's the same height above the outfeed table all the way across. Or below the table; it doesn't matter at this point. Then set the other two knives to the same height. Note that so far, it doesn't matter what that height is -- just as long as it's the same height for all three, all the way across. Finally, I adjust the outfeed table so that it's one-thou below one of the knives (any of the three will do, since they're all the same now), and go to work. No trial and error, no catches on the outfeed, no snipe on the trailing end, just a nice clean cut.