In King's gambit, is Fisher's conclusion that "3...P-KN4 ... is inexact" inexact? I was reading  A Bust to the King's Gambit by Bobby Fischer. The game starts with 

1 P-K4 P-K4 2 P-KB4 PxP 3 N-KB3


  [FEN "rnbqkbnr/pppp1ppp/8/8/4Pp2/5N2/PPPP2PP/RNBQKB1R b KQkq - 0 3"]


Bobby Fisher commented that


  "the move I played 3...P-KN4 against Spassky, but this is inexact
  because it gives White drawing chances in the ensuing ending: e.g., 4
  P-KR4 P-N5 5 N-K5 N-KB3 6 P-Q4 P-Q3 7 N-Q3 NxP 8 BxP B-N2  and now 9
  P-B3! (replacing Spassky ’s 9 N-B3) 9...Q-K2 10 Q-K2 B-B4  11 N-Q2
  leads to an ending where Black’s extra Pawn is neutralized by  White’s
  stranglehold on the dark squares, especially KB4."


It seems that the move 3...P-KN4 is still played frequently even today (even more popular than Fisher's recommended move P-Q3). So does this mean that Fisher's conclusion that "3...P-KN4 ... is inexact" inexact?
Apparently instead of 5...Nf6 in the line Fischer gave, 5...d6 6.Nxg4 Be7 is superior for Black.

You might look to Shirov for what is best in the King's Gambit.   He gave 1.e4 e5 2.f4? in his book and said "Prove me wrong".  In the past I saw him play a 3-minute game against 3000 rated computer on ICC in the King's Gambit and he crushed it.