From Year 607 BCE to 1 CE is 607 years
From Year 1 CE to 1914 CE is 1913 years
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Together adds up to 2520 years
That's their simplified math. But really, work back from whatever date you want and you can come up with whatever Bible math rule you want to create a cult date of significance. Look at 1975. All fuzzy math from the Bible and cult people applying it anyway that suits them. I find it hard to believe they forgot at one point that there was no year ZERO. It's almost like they don't really have "spirit-direction" and are just making shit up.