I must have missed something. Corbyn was committed to leaving the EU on the morning after the referendum and has whipped Labour through the lobbies.
That was just a rushed statement after an unexpected result, hardly a party policy.
“The British people have made their decision. We must respect that result and Article 50 has to be invoked now so that we negotiate an exit from European Union".
Putting pressure on the Tories - it's your mess, deal with it. It worked, the Tories are in disarray, they lost their majority in parliament, and more and more people are realising that Brexit is a bad idea.
Besides, Article 50 means nothing more than leaving the EU, there's no word in there about single market membership or anything else. This is what Labour voted for, regardless of how some are trying to rewrite history:
https://publications.parliament.uk/pa/bills/cbill/2016-2017/0132/17132.pdf"Negotiate an exit" on Labour terms, judging by the manifesto, may just as well mean "let's keep everything as it was, just formally remove us from the list of members". Labour also ruled out "no deal", meaning no exit until there is a deal, which could take decades, by which time another referendum would be perfectly acceptable to everyone.
"We need to look very carefully at the terms of any trade relationship because at the moment we're part of the single market, obviously, that has within it restrictions on state aid and state spending, that has pressures on it through the European Union to privatise rail, for example, and other services."
What's wrong with "look carefully"? And having looked carefully deciding that keeping all the benefits (i.e., staying in) is the best option. In any case, anything Corbyn may have said a year and a half ago cannot override later manifesto pledges.