Thanks for doing the calculations with the silph road calculator. This has become a semantic debate and I don't think anyone cares, but the IV is essentially an additive window of power, and 100% IV achieves the maximum of that window.
level 24 Snorlax
100% IV: 2134CP, 100% maximum possible CP, 100% of window
95% IV: 2120CP, 99% maximum possible CP, 95% of window
0%IV: 1850CP, 87% maximum possible CP, 0% of window
So the window size in this case is 2134 - 1850 = 284 (what you pointed out). The numbers for % IV match, like what you described. But for the full CP range a 95% IV will not correspond to 95% maximum possible CP, just 95% maximum possible CP contribution from that window, resulting in 99% maximum total CP.