Don't adjust the wiki just yet. I reread your initial post and found a flaw in your method. Here let me quote it, to start.
My pop_cap has been set to both 0 and 1 at different times, through numerous shutdowns and restarts, and I continue to receive migrants every single season.
In this world you have created, the pop_cap should have been set
hard during World Generation, I do not understand how you've changed theh pop_cap inbetween gaming sessions within the same region/world. Finn, how did you do that? Please explain how you change the pop_cap, which is set hard at worldgen when seeds are randomized and the terrain spline drawn. You are doing it inbetween your sessions? Or not? This is not possible as far as I know.
I would guess, side by side analysis, with two worlds, set with identical seeds but different pop_caps parameters would be more ideal for migration comparison and contrast. Embarks made at the same locations. Even then, the initial 7 dwarf attributes and world history results would vary inconclusively.
Maybe copy the region file, and play with two same histories? What do you think? I'd also be curious, what your [SET_LABOR_LISTS:SKILLS] were, as its my secret belief, certain dwarf skills are meant to appear on migrants, via their visits, at certain emergency times. Could just be speculation on my part, but when there is no pick, no anvil, and no traders on the horizon because of a low civilization world generation, a migrant miner, sure would be a gift from heaven.
Wishing you the best, Knutor
edit: paragraphing, and spelling, syntax