The reality is, unless a driver is being nit picky, they almost don't care or remember what pass you used when you got on, especially if there is a churn of passengers.
If i ever travel outside the boundary into Greater Manchester from Merseyside, i use my metro card to tap on at start point and have an already topped up bee card which you can stick tickets on at a local paypoint store and either get up and scan it when the bus flags change or if the driver confronts me about it of which a few have.
If a route I'm using goes into Cheshire or Lancashire such as the x1 or x2 or 7 to give a few examples, into areas which don't have all operator smart cards, I use my metro card to get to my destination and pay on my return trip or if the driver tells me to pay. For routes that start and finish in Merseyside such as the 300, or the 152, there is almost never any question as your pass is valid at the start and end of routes just not the middle! I once got the 152 to visit Halsall Church and then got the 300 and had to pay. If i had walked to Lydiate I could have scanned my bus pass.
I thought franchising would tidy this up and create a pass exclusively for both the region(merseyside) and the bus travelled on. I.e a pass which allows you to use non franchised routes but only up to the boundary. And any franchised bus wherever you board it! This would have been a step up over manchester which split tickets into two types, Bee Bus and Anybus. So much for 'Levelling up.'