There's a little bit of a philosophical thing here -- do you adjust the earlier measurement by some function because it's usually been high and revised downwards? If you do, you need to let every user know that you're doing something different, etc.

The worst case is that both the statistics orgs and the users are adjusting the numbers for a bias and overshooting.

This means there's a certain inertia: it can be better to handle the interim reports the same, even if they've been biased one way for several years, than to introduce a change that makes the numbers not comparable to history.

> 50% error.

It's not a 50% error; it's a 50% error in the magnitude of the change.

That's like saying that my room increased from 71.4 to 71.6 degrees, but my thermometer only saw an increase from 71.4 to 71.5; therefore, my thermostat has a 50% error.