The authors did state that they do not know of anyone who has exceeded the limit (which from what I remember was 2.5 RMR beyond 275 days. Read that on the writeup at Discovery magazine and I’ll try find a link for the quote tonight.
I tried to follow Amanda Coker’s Strava account to see her rides but she hasn’t accepted, so it’s hard to do any real number crunching there. However like Chris above is saying, I think she is one candidate who maybe has broken their limit and it could be a terrible oversight on their part, invalidating the study on the grounds that people simply haven’t been doing those sorts of efforts so they haven’t been able to plot that sort of data.