Gonna try, but I made a third file and I'm on week 148, no prompts this time. Also playing on a higher difficulty so getting these skills is taking even longer (strength is max, working on Linguistics). At this point I'm convinced that they just don't trigger if you reach a certain power threshold. In all 3 files, they trigger within the first year, or don't come at all, which seems at odds with their description as one would think they would be drawn to a powerful kingdom for more powerful men.
Edit: I got curious and slapped my save into the save editor a few times to check some changing variables and I noticed the oddest thing. It seems sometimes when you save and load, the displayed variable change. Sometimes I can see the total gold, sometimes I can't. Sometimes I can see various stats. Sometimes I can see my troop counts. They seem to change randomly. I'm beginning to wonder if some stats also turn invisible to Renpy as well, hence why the northern raiders didn't trigger at all in save 3. I'm gonna experiment with this line and load every so often.
Edit2: Didn't work, was a shot in the dark anyway.