There is a simple answer to the not so pedantic query.
Let's take a real world long ride as an example, which one, oh, let's choose LEL, as in 2017 that started in July and finished in August. For the purpose of the AUK event calendar and rider record it is a July ride, therefore counted in July 2017 for default RRtY validation.
Some riders wanted to have LEL counted in August which upon application to the secretary was duly granted BECAUSE they could demonstrate that they had ridden at least 200km of it in August.
Therefore, the default stands that the ride will count for the event start date, but, if you can demonstrate that 200km+ was ridden in a different month then your RRtY credit can count for your preferred month. However, that needs to be communicated in email to the incumbent RRtY secretary of the time and is at the secretary's discretion.
Please note: RRtY validation is still a wetware powered function, very little is left to care of machines alone.