Why are they even listing the +5 or +4 or +3 or any positive values of jumps with < or e (or both)?
Another easy way to solve this is that any jump called either of these things by the technical panel automatically voids out any positive GOE on the screen.
I get that sometimes skaters can have a million good things happening directly before the jump, in the speed/distance of the jump, and on the landing, but anything with one of these called errors should not get a positive GOE no matter what. I know that’s the goal they are somewhat going for, but just void out the positives so they are forced to mark more accurately and not ‘creatively’.
It's more accurate (as in comparing different examples of jumps with the same error) to allow for rewarding all the positive aspects of a jump as well as subtracting all the negative aspects.
Years ago some of those errors were listed as requiring negative GOE, but then the ISU explicitly changed those guidelines so that the pluses and minuses could balance out (usually to 0). Nevertheless, it's still very very rare for a jump with a rotation or edge call to earn positive GOE.
(And when that does happen, I suspect it's because the jump looked good to the judge in real time, they put in the positive GOE immediately, and they didn't notice after the reviews that the tech panel had added a call that required them to reduce the GOE. That would be an error on the judge's part. Yes, if the call could invalidate a high positive or flag a low positive/0 GOE so that the judge sees something flashing on the screen to let them know they should reconsider the mark they entered in real time, that would be a way to prevent this kind of judge error.)
What's new now is stating explicitly that certain kinds of technical errors, including the calls << and e, require that judges can only start with +2 on the positive side before they reduce for the errors. Since those errors carry penalties of -3 to -4, the final GOE is going to end up negative, although it could be as high as -1.
So yes, if it is not allowed to give positive GOE for an element with an e call, then there's no reason to include the positive GOEs in the scale of values.
Downgrades are not listed in the scale of values because their values are always equal to the same jump takeoff with one fewer rotations.
Yes, those calls could be linked to the judges' input such that scores higher than -1 would not be available to judges with << or e calls, with a visible alert to let judges know they have to revisit those scores.
The calls get added after the program, not in real time. So while the program is in process the judges would have access to the positive GOEs in real time.
There are other "significant errors" that are not called by the tech panel but that also now require GOE reduction after a maximum positive GOE of +2. So judges would still need to do the capping and plusing and minusing on their own for those errors.
Underrotations (90 to 180 degrees) are not listed as "significant errors" with a maximum positive GOE of +2. So it is still legal for judges to award high positive GOE and then subtract the -1 to -2 for the underrotation and still end up positive. Probably not higher than +2, though, because they wouldn't deserve the "Good takeoff and landing" bullet point mandatory for +4 or +5, so in practice the positive GOE would be capped at +3 before subtracting at least -1 for the underrotation. (And then they also earn lower base value, but that's not the judges' responsibility.)
ETA- in terms of evaluating an entire combination or three-jump combination with, let’s say a nicely done (as nice as it can be with the underrotation) 3Lz<+2T+2Lo, I still think the GOE shouldn’t be higher than -1 for the entire thing FWIW.
How about something like 3T+1Eu<+3S? That's pretty common -- how much do you want to penalize less than full rotation on a connecting hop between two otherwise beautiful triples?