It's all in the timing
"...another difficulty is that customer reference data and relationships vary over time. This issue has important implications for business intelligence applications that may analyze customer data across various time periods, comparing revenue this month to this time last year, for example. If, during the last 12 months, the customer hierarchies have changed or the sales organization has been restructured, then this will affect the validity of the comparison. This means that metadata and metamodel changes may have to be tracked and recorded in MDM applications."
Spot on Colin! Except that "may have to be tracked" should be "must". Organizations do not make significant changes to their business stcuctures every day, but these changes do happen every few weeks or months e.g. reorganizations occur, marketing reclassify their product hierarchy or customer segmentations, finance changes allocation rules. Yet most MDM products concentrate on point-in-time synchronisation e.g. of customer data, and frequently retain no history whatsoever. Hence when you want to make comparisons over time, or go back and reconstruct something in the pass to deal with a compliance request, the task is difficult to impossible since the old transactions may be archived, but the master data associated with them is typically not.
A well-designed system to handle master data should be able to reconstruct past hierarchies for comparison. Just as within a data warehouse, where you often want to go back and look at data "as is" and "as was" and even "as it would have been", the need to go back in time and understand the changes in master data is very important. However the big vendors don't understadn this issue properly, and most customers have just started dabbling in MDM so haven't thought yet about this thorny issue, which will come back to bite them in due course.