The thing is, all the GK knew about Shakky, and Luffy was mentioned by Sommers, so they´re clearly reading newspapers. I think Oda was just being dumb, because the Gorosei all knew about Jewlery Bonney pre TS, let alone the right hand man of an emperor involved in a major war on Onigashima,but it was a choice he made regardless.
Imo It really is just like SH, Except Luffy and Zoro, They knew or atleast had basic knowledge about what happened in their world, And people who is smart like Robin had the most knowledge of all.
so Some HK knew, Some HK don't.
The way i see WG is Gorosei and CP the smart one like Robin & Nami co, and HK is the brute just like Luffy and Zoro
Also the part of why some char were known by others and sum char is always happenin on every Anime especially battle manga.
Its like a trope if i would say so.
Baki is one of the perfect example of that.
I could see how it is weird about that tho so i agree that Oda was just being dumb lol