A minor disagreement...
>>>In SD, a RC of +4 after the first round is not the same as a RC of +4 after half the deck has been played<<<
Actually, +4 (the pivot point) is the only RC for which your advantage is the same no matter how much of the deck has been dealt; it is the equivalent of a Hi-Low TC of +4. For example, when a quarter of a deck has been dealt, a KO RC of +1 is a neutral count; if the RC is +4 at that point, the TC calculation is (4-1)/.75 = 4. When a half of a deck has been dealt, a KO RC of +2 is a neutral count; if the RC is +4 at that point, the TC calculation is (4-2)/.5 = 4.
With any RC other than +4 (the pivot point), your advantage or disadvantage varies based on how much of the deck has been dealt. For example, if a quarter of a deck has been dealt and the RC is +2 (the key count for SD), the TC calculation is (2-1)/.75 = 1.33. If a half of a deck has been dealt and the RC is +2, the TC calculation is (2-2)/.5 = 0.