Response code 409 instead of 404 when PATCHing against nonexisting resource?

The guidline mentions this:

If a service does not support UPSERT, then a PATCH call against a resource that does not exist MUST result in an HTTP "409 Conflict" error.

In the refered RFC 5789 there is this:

Resource not found: Can be specified with a 404 (Not Found) status
code when the client attempted to apply a patch document to a non-
existent resource, but the patch document chosen cannot be applied
to a non-existent resource.

I think this should be clarified, and the following should be added (according to RFC 5789):

Conflicting state: Can be specified with a 409 (Conflict) status
code when the request cannot be applied given the state of the
resource. For example, if the client attempted to apply a
structural modification and the structures assumed to exist did
not exist (with XML, a patch might specify changing element 'foo'
to element 'bar' but element 'foo' might not exist).

Start in Guidelines.md at the PATCH guidance linked from the issue, then compare its wording with RFC 5789. Clarify when a missing resource should return 404 versus when a conflicting resource state should return 409, and ensure the guidance matches the cited RFC.