I had half expected Corbyn to make a big thing of the risk that even if Johnson gets his self-styled microwaveable Brexit deal zapped and approved by MPs, such that the UK leaves the EU on 31 January, there remains a significant residual risk we'll tumble into something very like a no-deal Brexit by the end of 2020 - since it is stretching credibility that a useful trade deal with the EU could be negotiated and approved by then, for all that Johnson claims the contrary.
But Corbyn hardly bothered to highlight this risk, even though pretty much all we've heard from the Labour leader for months is how appalling a no-deal Brexit would be.
The reason, presumably, is that he would be highlighting how many years it would take to negotiate a meaningful trade deal with the EU, and that is as much a toxic sauce for his gander as for Johnson’s goose.
Or to put it another way, Corbyn probably doesn't want the brightest light shone on the implicit Brexit timetable in his plan to offer voters a choice in a referendum between remaining in the EU and leaving under a modified Brexit deal.
Because in the event that voters opted for Brexit in that referendum, which is promised by Labour for June, a Labour government would have even less time than Johnson - essentially no time at all - to negotiate a fully operable trade deal, if it wants to be properly out by the end of next year.
The point is that Labour’s version of Brexit makes it likely the UK would remain a non-voting, budget-contributing member of the EU - in “transition” - well beyond 2020, probably for the two years of extension the EU has offered and maybe longer still.
Which is not a version of Brexit that would be universally popular.
Or to put it another way, neither leader dares admit that Brexit is not a single moment in time, but a lengthy process of arduous negotiation.
Which makes it even stranger perhaps that Corbyn refuses to take the cleaner and clearer position of backing Remain, especially since so many of his colleagues were desperate for him to make that leap.
And of course it is striking that Johnson didn’t make a big fuss that Corbyn’s Brexit cannot be a clean break at the end of 2020 - because he is in something of a glass house when chucking those rocks.
So the hideous truth of an election that is ostensibly all about putting Brexit definitively behind us is that it can and will do nothing of the sort.
Watch the debate in full below: