I bet this wont happen. These historical buys/sells are static "on archive" information, thus running any active processing to them is unadvisable due performance reasons. When you look at them it takes miniscule amount of processing power, thus its insignificant. When you go trough whole record with compare search function its no more "minor" thing.
Its better to keep just the "on spot" information like game itself and current market on the caches of the CPU and RAM of servers and prune any secondary stuff away to ensure quality of service for core things.