Question about expected recursive resolver behavior

[Sarah Newman]

What should happen when for a given domain:

- The domain resolves via TCP but not UDP - UDP for this domain had no response at all.
- That authoritative nameserver hosts other domains, and those domains resolve via UDP.

I found https://www.isc.org/blogs/refinements-to-edns-fallback-behavior-can-cause-different-outcomes-in-recursive-servers/
but I'm not sure if this case is covered or not.

--Sarah