I don't believe there were ever any "factory" orange DK's. Especially since, by the time Jr. was released, DK had done its thing.
The problem with the cabinets for DK and Jr. is that they are identical in design, only the paint job is different, and it would be very easy for what was originally a Jr. to be converted to a DK (including swapping the serial plate on the back). The instruction sheet on the inside of the backdoor, if it's still there, may be a giveaway that an orange was originally a Junior.
People convert Jr.'s to DK's all the time for various reasons, especially over the last decade.