As I've said many times before, that serial number chronology produced by Lightner Library back in 1976 is next to useless. I have photocopies of a lot of the tabulation sheets Roe Clark used to do the 20-gauge tables in McIntosh's book. There are nine XE-Grades in that block of 100 serial numbers, five marked down as "XE Spec." Three of the nine Roe couldn't read a complete date off the card, and the others range from January 1921 to July 1924.