Three Fields That Decide the Outcome
Still open
Start by pulling every existing record into one sheet before changing anything.
Refreshing without drift
Nine times out of ten, beyond that anything unverifiable should be removed rather than corrected.
In the file
Put plainly, set aside time to rebuild on a fixed schedule rather than treating it as a one-off project.
Out of date
Beyond that a workable routine is to review twice a year and log every change with a date.
Worth checking
Even therefore, work from the aggregators outward, because fixing a source fixes everything downstream.