minConvertibleEnglishDate

Earliest English date that converts, matching startingEnglishCalendar.

The two calendars start mid-year relative to each other, so EnglishYearRange alone is not a sufficient bound: 1913-01-01 through 1913-04-12 are inside the year range yet have no Bikram Sambat equivalent. A Gregorian grid shows those days disabled rather than hiding the month.