Stealth & Sleepy - Welcome!
I, too did my research the old-fashinoned way - before the advent of the Internet, only most of it was while I was in the Bethel libraries. I was raised a Dub, & was also determined not to use "apostate" materials to find out the truth about 607. Like you, I couldn't find any credible support for that date. That was to be the first crack in the dam, so to speak. Couple that with the weirdness that is Bethel, and I was well on my way out. I left in 1993, and it was the single best decision of my life!
Again, a hearty welcome to the board - we all look forward to seeing more posts from the both of you. You'll like it here...
--Michael