Question about parent-to-child inherited real estate [View all]

So heres a question about inheriting real estate in California.
My mom died in 2024, and her living trust said her home would go to us 3 children. I was living in the home, after being her caregiver for 11 years. I processed all paperwork at county assessors office for the parent-to -child property tax exemption (so the house wouldn't be reassessed). The next tax bill did not reflect reassessment so we thought everything was okay.
My brother, the executor, recently received a letter from the assessor saying the house would be reassessed, because they don't have the forms I did.
My brother, sil and I go to their LA office ftom Carlsbad. They tell us about Prop. 19 from either 2020 or 2021, that did away with that exemption! Luckily I was living in the house so they will
likely halve the assessment, but will still be alot. Neither my moms estate attorney nor my brothers tax accountant told us about this. My mother could have put our names on the title.
Question: how is this not malpractice?
I don't know if I want to sue anyone, I'm just pissed.