I've corrected the first date comparison to be ">=". Thanks for pointing that out. >'Date("192X-XX-XX")' denotes the interval [Date("1920-01-01") ... Date("19

I've corrected the first date comparison to be ">=". Thanks for pointing that out. >'Date("192X-XX-XX")' denotes the interval [Date("1920-01-01") ... Date("1929-12-31")] The partial date is not the set, but a single date that is in a set. There is notation for sets of dates: # Each means a single day in the 1920s 192X-XX-XX [1920-01-01..1929-12-31] # A collection of all days in the 1920s {1920-01-01..1929-12-31}