The Wikipedia article on Jet ( https://en.wikipedia.org/wiki/Microsoft_Jet_Database_Engine https://en.wikipedia.org/wiki/Microsoft_Jet_Database_Engine ) talks a

The Wikipedia article on Jet ( https://en.wikipedia.org/wiki/Microsoft_Jet_Database_Engine https://en.wikipedia.org/wiki/Microsoft_Jet_Database_Engine ) talks a bit about the backwards compat strategy. This is case where they broke backwards compatibility. At the time, they had an upgrade strategy, though I wouldn't be surprised to learn the tools that handle the upgrade are no longer supported at this point. My understanding from the outside is it was an attempt to bring Jet Red (the desktop database, what Access used) and Jet Blue (the server database, used by things like Exchange) closer to be compatible with each other on some level, along with making Jet Red less of a "toy" database.