Yes, the 20th C helmet is only one of many tour helmets that were made over the decades. There were tour helmets produced after ANH (the source of the Rick Baker mold), tour helmets made during ESB and RotJ --the RotJ helmets typically have the tall "pipe" style connector as seen in the ILM book (there is a photo with a table full of tour helmets/chest boxes/belts being made) and the DPDeluxe. The 20th C helmets were made in the mid 90's by Don Bies to promote the Special Editions and were just the first to fall into fan hands to be copied.
I have a copy of the most recent version of the lineage chart: