A teacher once told me that the greatest professional musicians in the world still make about 3% error - despite an infinite amount of practice. That is, they mis-play about three notes out of every hundred. If you look at Tegatana no kata, it has between about 70 and 100 steps (depending on how you count it). This implies that there will always be a few missed steps each time you do it even after you have practiced it for years. Thus there will always be something to work on in this exercise.
Something to look for is the difference between systematic error (bias) and random error. When you spot one of those mis-steps, are you making that same mistake repeatedly or was that just a fluke? Systematic error is (perhaps) more shameful for the expert but it is by far the easier type of error to fix. Errors that occur at random are hard to pinpoint, much less fix. Errors that you make repeatedly the same every time are pretty easy to modify, but to fix a random error you have to re-tool your entire thinking process and movement strategy to be more error-tolerant or error-detecting or error-correcting. Change everything that you do so that there are no consequences to the occasional random error and suddenly the error will cease to exist. This is why the greatest experts can do things that are taboo for novices – because some of these things make a difference for novices but don't matter for the expert that has worked through that particular error for years.