Here's a bit of his early history...
During the '60s Charles Thomas sang with a group called the Mystics (later changing their name to the Dealers) on the King Record label. In 1969 he joined the Drifters, adopting the nickname Don to avoid confusion with Charlie Thomas who had been part of the Drifters' line-up 1958-67. Within months of him joining, the Drifters broke up.
http://home.att.net/~uncamarvy/DriftersLate/dr ifterslate.html
Not sure what happened to Don between then and the original '74 release of "Come on Train" but around this time various splinter versions of the Drifters came into being (including
Charlie Thomas' Drifters - NB the "original" Charlie not Don) which eventually led to lawsuits over use of the name.
Don obviously could not keep away from the tribute band cash cow as it is possible to book
Don Thomas And His Drifters Review...
http://www.locoloboevents.com/loco_tribute.php ?type=&offset=100