Nah I think you are doing okay with the coal. The big closing down of the mines was in the 80ties under Thatcher, so people were using it still at that time.
And as for au, for me it works as long as the canon characters are IC and the story is believable - and for me that's more important than canon accuracy. For instance: letting them go to Brighton with its mixture of working-class holiday visitors, bohemian atmosphere and gay and lesbian friendlyness feels just right. And that is more important to me than the fact JKR situated Severus somewhere in the North, way too dat from Brighton.