Our first year we got about 45% of our student population to complete the Annual Update, and this year we pushed hard and got it to ~75%. We were also complicated this year because we moved from in-district hosting to cloud hosted, so our IC URL changed and a large number of families couldn't log into their parent accounts to complete the Annual Update. I don't know if we'll ever hit 100%, but next year we are hoping for at least 85%.
For the population who didn't complete the Annual Update, we had the building secretaries manually follow up with each family to collect their proof of residency, as we at least needed that.
I think what others have said is also true: it's a multi-year process that will take a lot of involvement with other people outside of Tech. Admin need to be on board, secretaries need to be brought in, we're even looking at hiring a summer stipend position to follow up with families who need the extra attention, etc.