I believe the C135 (KC135) was originally called Boeing 717.
True of False?
The KC135 was derived from the Boeing 367-80 (the prototype for the 707 as well). The KC135 never carried the 717 designation within the Boeing Company. The fact that Boeing skipped past it with the 727 introduction has been the source of this "urban legend" that has been the cause for some, even within Boeing, to refer to the KC135 as such. I am quite sure that there has never been any Boeing drawing, manual, or other such documents that attach "717" to an aircraft prior to adopting the short haul DC9 after the merger with MDC.
There is no rational pattern to the model numbers assignment