I think the confusing issue is that what will become connect routes may get other stock in the interim period such as 170's and 769's.
It's been reported 769s will work Windermere services for 18 months before it becomes a Northern Connect route, while 170s earmarked for Harrogate line services will be used on Calder Vale until 195s are introduced.
I guess its also possible some connect trains will work some non connect services especially the 331 EMU's
In the case of 331s that's not a possibility - that's a certainty. All 158s are being done up to the same specification so technically you could say that also applies to any 158 working a non-Connect service.