Tell them (or your attorney) their meter readers and billing system have recognized the moved meter for decades. They wouldn’t if you or your parents had installed without authorization.
if they don’t have a record ask for rebate on bill payments.
Correct.
As a former meter reader in the 1980s it was one of my duties to report any irregularities. Example: I had people fully enclose a meter inside of an addition between monthly reads and I had to report it. Moving a meter around as described in the OP should have triggered such a report. The fact that it apparently didn’t goes strongly to the fact that PG & E did it.
Common sense right there.They will never go for it.
Ditto what you said: They have ‘read’ the meter in that location for forty years and never once complained.