From the lack of response I'm assuming this is an edge case not many have had to find a solution for. I've posted similar on a Facebook group specifically dealing with SINP and also didn't get any answers there.
So for SINP EOI we have decided to just claim for the 8 years for now and look to getting a job offer to bolster points.
For the EE application case would still appreciate some insight regarding whether we need to specify and prove employment which is further in the past than the previous 3 years? How far back do you actually need to go?