1GBC 1921 Southbridge, Massachusetts

Operator: William E. Arnold

Three letter callsigns in the 1st District were changed on July 1st, 1921.
Apparently when they ran out of two letter callsigns and started using three letter callsigns they kept the middle letter constant and changed the first and third letter.
His callsign switched to 1BDC after July 1st, 1921. It appears he was active until 1925 or 1926 then no longer appears in the callbook.
Starting in 1937 and into the 1940's William E. Arnold shows up in the callbooks as W8LJT in Cleveland, OH. I have to assume it is the same person but can not be 100% sure.
In 1921 he won a prize for copying President Harding's message sent out for Washington's Birthday on February 21st, 1921.

QSL, Info courtesy of N2BTD