It sounds as if you have solved the immediate problem.

In case anyone else comes to this thread seeking clarity about the fairly complex Availability filter, the following definition can be found in a draft FAQ at http://bit.ly/OF-QL.

Available: Tasks which are neither waiting their turn in a sequential project, nor already completed, nor deferred by a future start date (either of their own or inherited from a project or Single Action list), nor out of action because their project or context is on hold or dropped.

More formally, using terms from the Applescript library:

[Available]->(blocked is false) and (completed is false) and ((start date is missing value) or (start date < now)) and ((its containing project is missing value) or (status of its containing project is active) and ((start date of its containing project < now) or (start date of its containing project is missing value))) and ((its context is missing value) or ((allows next action of its context is true) and (hidden of its context is false)))