You're not understanding my point. The Sherlock Holmes Universe is different to the DWU. Fact. If they were to make a crossover.... then what? There's my point. If the Brigg's Sherlock popped into TARDIS and shook hands with Twelve, it can't possibly be valid, right?
Well it's a story, so it passes rule 1. If it's licensed by the BBC, it passes rule 2. When it's released, it passes rule 3. It's intended to be set in both universes, so it passes rule 4. Now d'you see my point? When two incompatible universes combine yet pass the four rules, as may Looking for Pudsey, then we have to maybe bend or ignore the four rules.
My point makes perfect sense and is totally connected to this discussion. I gave further examples, such as Assimilated and the Marvel story, whose name escapes me. This seems to fall into that category of stories that can't follow the four rules. We need an admin to input their take on this.