How important is ‘authenticity’?

Problem:

1. I want to write a crime series based in Cumbria.
2. I want to have a female detective, who needs to be at least at sergeant and better still at inspector level.
3. I want to keep clear of the technical complications of the DNA, Police and Criminal Evidence Act and the introduction of computerised data.

But… there were no female detectives in Cumbria until the 1990s. So, something has to give. Does authenticity matter, or could I introduce a female detective earlier than it actually happened? Ironically, the Cumbria police force now has plenty of high-status female detectives, including one with the wonderful surname of Thundercloud, but this is now and that was then. So what to do? My reluctant conclusion is that authenticity does matter: I must stick with my physical setting of West Cumbria because it’s so important to me, and so the time setting has to move into the mid/late 1990s. All the necessary research is unavoidable, but I can do it. Should be fun to discover how life has changed over the past twenty years.