Just playing around with two different G tools I'm reminded of how little it matters that predict figures are accurate. What matters is that they are useful. Eg, here are monthly predict figures for two G tools:
Keyword: business development manager
* On the External Keyword tool: 2,400
* On the new search-based keyword tool: 8,200
Access the new tool from with in an Adwords account on the tools page.
There are bunch of other reasons why why you don't need to fret about accuracy. I'll come back and list them soon.