Tim,
Right, Epicor has documented that the SSR is not a subledger to the GL. See KB0034343. And backdating it is also just for curiosity. It’s not designed for perfect accuracy. It can’t. Things like changes in standard costs and qty-bearing (mid-month) will make it confusing, to say the least.
The article is pretty explanatory and Mindy, the author, is an excellent support rep.