No hitters are kind of a separate category anyways. Similar to scoring 50+ points in a basketball game or throwing for 5 TDs etc. They are in the history books but it's not a typical stat tracked on every player or team page. It's more of an anecdote to a season or a career. So I think you just add an asterisk that it was a combined and list all the pitchers involved.
Yeah Justin Verlander has thrown 3 no hitters when he gets elected to the hall of fame that will be a notable accomplishment but if they were 3 combined no hitters maybe it shouldn't be.
No hitters are kind of a separate category anyways. Similar to scoring 50+ points in a basketball game or throwing for 5 TDs etc. They are in the history books but it's not a typical stat tracked on every player or team page. It's more of an anecdote to a season or a career. So I think you just add an asterisk that it was a combined and list all the pitchers involved.