It used to be that International weekly e-fare specials had very specific wording that stated that they were not upgradeable, up front not in the fare rules.
I reviewed the International weekly e-fare specials rules many months ago and found this wording about 'upgradeability' was no longer included.
I assume now that the fare class is the deciding factor. So e-SWU's "... may be used on most United Business (C) or United Economy (Y, B, M, H, Q, V, W) booking classes. ...except when the terms and conditions of sale state that the fare is not eligible for upgrade. "
So if you purchase an International e-fare weekly special in CYBMHQVW, and there is no wording in the fare rules specifically excluding upgrades, you should be good to go?