I think the main thing to realize is that - for whatever reason - some mounts do not go exactly where they tell themselves to go to. I don't think a model or backlash is involved at all. That is why I keep emphasizing the view of a missile. If a missile misses a moving target - it may have a perfect model and no backlash - but the goal of reaching a certain point at a certain time quickly is not trivial. And that is why there used to be a thing called GoTo calibration in celestron mounts - and that is what the firmware designer has conveyed.
Backlash is easily removed by winding way back and then forward. That is how celestron mounts work - and I can't imagine a mount that didn't do that in a slew - except one with high res encoders.
The real reason you know it isn't backlash is that backlash alone would give perfect encoder readings - but a physical offset in pointing direction. That's because mounts like these have encoders on the motor shaft and before the gears. The encoders do not see the backlash. If the encoders are wrong - in terms of ra/dec - it is not backlash.
What we have are a set of mounts that - for some reason - do not goto exactly where they are told - and they miss by a consistent amount.
So is anyone able to try Jared's recent code? I cannot - unfortunately - for some time. But if it works - it works - and people should be able to check.
Frank