The ASF doc on the NOTICE file states:
2. The remainder of the NOTICE file is to be used for required third-party notices. The NOTICE file may also include copyright notices moved from source files submitted to the ASF.
I understand the part about "copyright notices moved from source files" but what are required third-party notices?
After participating in many Incubator poddling release reviews I've seen poddlings asked to do release respins because they've left stuff out and also to respin for including text that is said shouldn't be included. There doesn't seem to be much common understanding on what these notices are, and like LEGAL-31 this is a constant point of contention at the Incubator so it would be really helpful to have some clarification.