Don't know how back you're going into the historical data but maybe 6 or 7 years ago there was a major distance remeasurement programme across all GB tracks.
Distance that hadn't been that precise to start with (typically rounded to the nearest half furlong back in the day) were remeasured using some proper 21st century kit, current rail alignments, standard measurement rules (i.e. racing line distance from rail) and so on.
This led to race distances at a lot of courses being restated without any actual on-the-ground change. Some reported distances changed by 30 or 40 yards, from memory.