In any prosecution under this title where the grade or degree of a crime is determined by reference to the degree of a felony for which the defendant or another previously had been sought, arrested, charged, convicted, or sentenced, if such felony is defined by a statute of this state which is not in Title 9A RCW, unless otherwise provided:
(1) If the maximum sentence of imprisonment authorized by law upon conviction of such felony is twenty years or more, such felony shall be treated as a class A felony for purposes of this title;
(2) If the maximum sentence of imprisonment authorized by law upon conviction of such felony is eight years or more, but less than twenty years, such felony shall be treated as a class B felony for purposes of this title;
(3) If the maximum sentence of imprisonment authorized by law upon conviction of such felony is less than eight years, such felony shall be treated as a class C felony for purposes of this title.