The following is just speculation about he CTR arrived at the date of 1914 initially.
I was wondering if CTR was not trying to reverse engineer that date. I think he already had 1874 as Christ presence, and I believe he added 40 years to that due to some Jubilee rule. Not sure, SO,... SO,.. he used the 2520 years from William Miller to start looking backwards to see what Bible event happened around that time so that he could start counting forward to be able to justify his date of 1914. 586 or 587 BCE was close enough to work with to hitch his beginning date to.
NJY