i think you confusing things, things that individual FLD’s make up and those that comply with within the law and HO statutory guidance.
But it’s only guidance, not law. Guidance is a suggestion, like a picture on the back of a pie box showing it on a plate with some chips and peas - you don’t have to eat it with these other foods, but it’s a suggestion.
Statutory Guidance - statutory means it is a legal thing.
The guidance to the Chief Officers on firearms licensing is statutory, the Guidance on Firearms Licensing is not statutory (although it does contain a lot of legal stuff, much like the Highway Code), but is considered best practice, and it can be deviated from in special circumstances (chapters 1.1-1.4 explain this). Generally it should not be deviated from (1.2) as one of its aims is to promote consistency across force areas (1.1).
The trick is to ask nicely why the best practice (ie The Guidance) was deviated from in a particular circumstance (1.2), and asking for the justification in writing is usually enough to 'correct' an issue or at least mitigate the problem that caused it in the first place. If you know the problem you can possibly fix it.