Hi Kristen,
The JDE date format is CYYDDD, where:
C is added to 19 to create the century, i.e. 0 + 19 = 19, 1 + 19 = 20.
YY is the year within the century, DDD is the day in the year.
This formula will create you a column transfering the JDE into Gregorian:
Table.AddColumn(Source, "Date", each
#date(Number.From(Text.Start([Julian Date],1))*100+1900 + Number.From(Text.Middle([Julian Date],1,2)),1,1)+
#duration(Number.From(Text.End([Julian Date],3))-1,0,0,0), type date)
Regards,
Matthias