This issue doesn't have a moderator - I think that's why it's not progressed. I 
will moderate it. @snowman2's current proposal 
(https://github.com/cf-convention/cf-conventions/pull/282) is to replace

However, in those situations where two values of a given property are 
different, then the value specified by the single-property attribute shall take 
precedence. For example, if the semi-major axis length of the ellipsoid is 
defined by the grid mapping attribute semi_major_axis and also by the crs_wkt 
attribute (via the WKT SPHEROID[…​] element) then the former, being the more 
specific attribute, takes precedence.

with

If both crs_wkt and grid mapping attributes exist, the attributes must be the 
same and grid mapping parameters should always be completed as fully as 
possible. As such, information from either one (or both) may be read in by the 
user without needing to check both. However, in those situations where the two 
values of a given property are different, the CRS information cannot be 
interpreted accurately and users should inform the provider so the issue can be 
addressed. For example, if the semi-major axis length of the ellipsoid is 
defined by the grid mapping attribute semi_major_axis and also by the crs_wkt 
attribute (via the WKT SPHEROID[…​] element), the value of this attribute 
cannot be interpreted accurately.

I think this is OK, except for the last sentence, which I think should be

For example, if the semi-major axis length of the ellipsoid is defined by the 
grid mapping attribute semi_major_axis **disagrees with** the crs_wkt attribute 
(via the WKT SPHEROID[…​] element), the value of this attribute cannot be 
interpreted accurately.

That leads naturally to the unaltered final sentence, "Naturally if the two 
values are equal then no ambiguity arises."

Philip @cameronsmith1 and Karl @taylor13, are you content with this? Alan 
@snowman2, is my amendment OK with you?

Jonathan

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