Hi @ChrisBarker-NOAA : can't we keep the de-fact definition of days in the 
Gregorian calendar being exactly 86400 seconds? Precision in the standard is a 
good thing. Clearly there will be less precision in the time values entered in 
many cases, but that is up to the users who will, hopefully, provide the level 
of accuracy required by their application. This would make `gregorian` 
equivalent to `gregorian_tai`.

You ask why it matters to the convention that the UTC calendar is not defined 
into the future past the next potential leap second: this is an issue of 
reproducibility and consistency. The changes are small, but we are only 
introducing this for people who care about small changes. The ambiguity only 
applies to the time-stamp: the interpretation of the statement `x seconds since 
2018-06-01 12:00:00Z` will not be affected by future leap second, but the 
meaning of `y seconds since 2020-06-01 12:00:00Z` may change if a leap second 
is introduced next year. One solution would be to disallow the use of a 
time-stamp after the next potential leap second.  

I agree with Chris that we can't hope to retro-fix problems which may have 
occurred due to people putting in information inaccurately. What we need is a 
clear system which allows people to enter information accurately. 




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