This looks promising , nice job.
Its hard to say exactly what weed roots may have survived, I am guessing you started in July or early August? They have been trying to grow in darkness for say 4 months, and using up their energy.
Most look dead from the bottom photo. Yes some weak couch grass is still there, much weaker than before. To have composted and recover over winter is excellent.
If you look under the mypex in March and see no white shoots of couch, you could grow without it. Or plant through and pull any couch you see regrowing through the planting holes. Same for other weeds like bindweed.
Thanks too for sharing the costs. It looks reasonable to me for the time saved (ongoing) and potential increase in output. Yes mypex is pricey but is usable for 10-15 years from reports I hear.