The British Museum have at least two impressions. Boston have five, showing a cycle of three the last time "it" was on view. So viewings can be more frequent th

The British Museum have at least two impressions. Boston have five, showing a cycle of three the last time "it" was on view. So viewings can be more frequent than the 4 year gap, or they can keep the gap and have a longer exhibition. Either way, more people get to see it.