I worked on the notion that Runners developed skills, especially in knowledge, in an eclectic and/or tacit experience kind of way. Different approaches of development to ultimately a same level of understanding.
Your runner with Gang knowledge might have gained that in several ways. Maybe they lived street. Maybe they lived as a cop. Maybe they did a comparative analysis of the sociological conditions associated with disenfranchisement as it relates to locked upward mobility and lateral options. And then what would be different is that 1st guy has Etiquette - street gangs, 2nd has cops 3 has academics....or something like that.
Knowledge (and skills in general) in 5e and before rarely, if at all, dealt with the reality that skills and knowledge fade and become obsolete in cases if you don't keep up with them. Oh you have a knowledge 5 rating from stuff relevant 25 years ago? Yeah that's only a 2 now if you don't pay these upkeep costs. I mean literally for my profession (social work) for license stuff they can decertify you if you don't keep up with your CEUs (continuing education units)

And talking about Social Work as a knowledge, there probably aren't many of us with too high a base Social Work knowledge. Why? Because at higher levels you specialize. Functionally, knowledge wise, I'd say a BSW "social work" knowledge isn't that different from an MSW "social work" knowledge, but the MSW guy has more depth in multiple knowledge areas (theoretically, I've met MSW that I'm amazed even made it out of school....) I can tell you basic principle stuff re: Gerontology field as it relates to SW, or some of the substance abuse stuff, but my stuff was more child/adolescent mental health, early childhood, CWS, etc. The guys that concentrate on Macro tier SW have different knowledge sets than those that work Front Line field.
anyway
I think we can all agree the skill system in ANY rpg isn't 'realistic' and shouldn't be. The trade off in hyperspecificity to try and get things as accurate as possible....probably doesn't matter.