Well, actually it does matter if the film is intended to be taken seriously as documentation of the sequence of events leading up to and including the Dams Raid.
Well, it's not is it? It's a film.
In any case, as someone who has a degree in history, I am aware that there are many historical details of which you (and indeed I and just about everyone here) will not be aware and would not notice if they were different: the colour of the chair that Character A sits on, the make of typewriter used by Character B, etc. These are all historical 'facts' but not being 100% accurate makes no difference to our understanding of the broader 'truth' of the events (if that's what you are interested in) - just as it wouldn't matter in a drama about the Shoah whether a particular character who dies was called Goldberg or Goldblum. In addition, there are too many 'facts' to put into a feature film or even a documentary - they are always selective and decisions have to be made about what is important or not.
If it matters that the dog's name is the same as a codeword used, then so long as they are the same, it doesn't matter what they are. If the death of the dog is important, it still doesn't matter what the dog's name is. So, if it is going to detract from the main truth which you are trying to get across, we shouldn't be too hung up on minor facts.
It would be different if one of the main points was to bighlight the changing attitude to race in the RAF or in Britain generally - but it isn't, is it?