Grief with Exported Asana Tables

I am working with a client that has exported Asana tables for projects, tasks, stages, notes, and tags.

Four questions that answers would be definitely appreciated.

In their exported tasks table, the task ID column is not a unique row identifier (but project ID + task ID appears to be). In other words, a single task ID can be assigned to multiple projects. Is this normal for Asana?

In their exported stages table, there is only a reference (foreign key column) to a task ID. Repeated requests to also export the project ID column appears to fall on deaf ears. Is a project ID column not available in the stages table?

If a project ID column is not available in the stages table, is there another way to link a stage to a single row in the tasks table?

Is there a url where I can view the data structure of the base table configuration (tables, columns, relationships, and data types)?
Any help in answering these questions will be appreciated.