I know the Bob Graham round has a long history, first completed by the man himself back in 1930s (I can't recall the exact date) and whilst not a typical "race" can be found in many race calendars under "individual attempt". Along that line many of the northern fell races have a long history too, dating back to late 1800s, Grassmere and Borrowdale spring to mind.
"Q. Are there any exceptions to this rule? A. Yes, the committee has decided that the long running Windermere 10 Marathons in 10 Days challenge shall continue to be counted as 10 separate marathons for 100 Marathon Club purposes. The reason we are saying this is that each day is in fact an exact measured road marathon of 26m 385y, still upholding the integrity of the marathon. Other events will only be considered as exceptions if they meet these criteria."