Sounds like a lot of us were either shouting at the TV or at least grumbling internally about the apparent "leaps of faith" in this episode. As someone who has family from Staffs I wondered why they showed the census & marriage certificate at the William Salt Library when it is the Archives (virtually next door) that has census access & parish registers (though this copy of the cert had been issued by the registrar at Cheadle).
As I record the programme I went back to the point at which the marriage certificate of William Roache's parents was shown & one of the witnesses was, I think, Lillian Radcliffe Stanier - presumably one of the family that William's mother was with on 1901 Census night. Incidentally Leigh, Staffs, where the Staniers were in 1901 is close to Alton and was where Zillah was from (not sure that was mentioned).
I know the series is aimed at a wider audience beyond keen family historians, but this particular season seems to have had more unexplained leaps & assumptions than previous ones - a little more in the voiceover could go a long way to making it clear the "other research has shown..." even if the footage to support it can't be shown.