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Anyone who joined to vote for Corbyn will vote for Corbyn regardless of what he says about Brexit. He could win on his current base regardless.
Anyone who isn't sure, possibly including: long term Labour members who may have joined under Kinnock, or may have left the party but rejoined recently, the traditional working class base, mainly from the North, most of these people will have voted for Brexit. So Corbyn has played it quite cleverly here: being ambiguous over brexit, and then declaring he respects the vote to leave, gives him a win / win situation.
Smith's suggestions of ways to block or delay Brexit, versus Corbyn saying the vote should be respected, has I think just won Corbyn the election, in case there was still any doubt.