Ah the professional sicknote, every workplace has one or more of them! They somehow managed to navigate and confuse HR departments interpretation of said companies sickness absence rules and string out their pointless existences for years at a time.
Yes there's plenty of these around who know how to play the system. I used to work for a company which dealt with occupational health (see much earlier in the thread, the company with DOGS). It was quite amazing to see the size of an industry which is effectively built around trying to get sicknotes to go back to work. Some of the acceptable reasons for taking long term leave are quite staggering.