Why two cuts across the throat?

[kensei]

My guess would be because the Ripper had never cut a throat before Nicholls, and wasn't sure of himself yet. I believe that Martha Tabram was his first murder, and the mad stabbing spree he unleashed on her would have spattered him with blood quite badly, leading him to try a different technique in his subsequent attacks, and his hand became steadier with each time from that point.

[IchabodCrane]

Why do Nichols and Chapman have two cuts across their throats, but Stride and Eddowes only one? Does anybody have a theory on that, and what it could reveal about the MO?