yeah, dont be too strict with lore.

have you noticed that there are super mutants across from california to DC, yet people from Pitts never heard of it?

It is possible that The Pitt has not seen super mutants. The super mutants in california are different from the DC ones, a product of different FEV Strains. The Super Mutants from California did move east after the Master was stopped in F1. It is possible that they were stopped from moving as far east as Pittsburgh and DC by the Midwestern Brotherhood of Steel as seen in Fallout Tactics. I was surprised that there were no Old super Mutants from California in F3.
As for the New DC Super Mutants, it is not known how many of the New Super Mutants of the DC strain of FEV were "made." They seemed fixated and happy to stay in DC close to their vault and source of FEV. Which by the game time 2277 the vault was out of DC FEV.
The people of the Pitt also seemed to be fixated on staying in The Pitt or are enslaved so they can't go out side of the City. Anyone that does escape or has the sense to leave would most likely not want to come back to tell of super mutants of any kind.

I know this is off topic sorry
I agree with you about being to strict with the lore and the F bible. If I am being a buzz kill, sorry my bad, I am working on trying to stop

I know it's an Easter Egg reference to FO2, like where you literally find an Easter Egg. But seriously, you had to help the Junktown Jerky Guy in FO2 as a sidequest. Remember how he said he wanted to write down all his crazy stories?

Different strains of supermutants entirely.