Good to know the number visible can be tuned and the number retained is much higher.
The background on what raised the question (i.e.; can it be extracted) is the desire to do some longer term analysis of workflow execution history. Use-cases include: a customer might capture a trouble ticket number field in a workflow (as a WFA UserInput) and later want to search WA workflow execution history to identify workflows referencing a set of ticket numbers (by looking at UserInput field value). Or, what workflows provisioned into a certain aggregate (by looking at Execution plans) of historical workflow runs.
The solution to these use-cases doesn't have to be 'to extract execution history' but I'm looking for a solution that allows programatic access to scan WF Execution history and works without concern of WFA purging exec history before our processing logic gets a chance to run. So I'm researching to find out of what we see in the Execution tab Execution History is a table in a database somewhere, or a set of XMLs files in a directory somewhere.