This may not quite be what
@Simon75 was looking for, but in the 1980s and early 1990s, Sunday services in the Medway Towns operated under a completely different series (120-129), with little reference to the weekday routes. These were often cross-town, so areas had direct services on Sundays that meant a change during the week, but direct on Sundays (regardless of whether it made any sense or not).
Although they were all operated by Maidstone & District to start with, the tenders were then won by a variety of operators, seeing such things as Kentish Bus operating in Rainham, or Chalkwell in Gravesend. (I'd have to look up exact details). So different route, depot and company, all just because it was a Sunday!
I understand the PVR of Gillingham depot is now 41 on a Sunday, and all routes follow the weekday alternatives: quite some change in the years since Sunday shopping was introduced!