I don't think indexes were designed to be relied upon. If you need a reliable name for a source/sink, use a predetermined, unique name.
Oh, one other thing. Indexes seem to be autoincrementing, and are automatically adjusted if you remove a sink or source at runtime. So you would have to modify the PA sources to change indexes from their current behavior of just assigning a tracking number to sinks/sources, to being a meaningful datum. But doing that is redundant, since we already have a uniquely-identifying, meaningful field for sinks and sources: name.