I believe JT5DX is the contest callsign of JT1CO. Different QTH and a first class contest station.
wow, judging by the email JT5DX lists on qrz, he *is* JT1CO. I wish he would upload his JT1CO contacts to LoTW as often as he does his JT5DX ones. It has been 2 years since JT1CO uploaded