It was a tale of two votes last night. The first didn't happen – the government retreated over reproductive rights rather than be defeated on Stella Creasy's amendment, meaning Northern Irish women who travel to England to access an abortion will receive NHS funding.

The second was a thumping endorsement of the government's EU exit strategy – just 101 MPs voted for Chuka Umunna's amendment regretting that the government had not set out plans to remain in the customs union or the single market. A mere 49 Labour MPs joined the rebellion after the party's leadership ordered them to abstain – with even some of those who had seconded the amendment falling in line, though four shadow ministers lost their jobs rather than follow the whip.

Why did one amendment succeed and the other fail? One red herring is the Euroscepticism of Jeremy Corbyn, the Labour leader. Corbyn is a Eurosceptic of long vintage, of course, but Theresa May has a history of voting to limit reproductive rights, and that didn't stop her opponents getting their way yesterday.

The truth is that – just as with the Article 50 vote last year – Corbyn's decision probably changed a handful of votes either way. Left to their own devices, Diane Abbott and Barry Gardiner, plus perhaps another 20 or so backbenchers, would have voted for the amendment.

But as it stands, a far bigger rebellion would have gone the other way. Whether through conviction that Britain does need to get its immigration under control (Caroline Flint, Stephen Kinnock), the belief that the referendum was a de facto one on border control so, like it or not, that must happen (Jonathan Reynolds, Emma Reynolds) or a belief that Labour must toughen its policy on immigration to win an election (Yvette Cooper, Tom Watson), there is, at present, a large majority within the PLP for a drastic breach with the European Union.

That doesn't mean that Britain's single market membership is doomed. That the 49 Labour MPs who voted on Umunna's amendment span the breadth of the party, from Kensington MP Emma Dent Coad on one end to Alison McGovern on the other, shows that Labour's single marketers have the potential, at least, to unify and convince much of the PLP.

They have the added benefit, too, that most party members are pro-EU, and most of the trade unions are in favour of retaining single market membership.

So why can't they make a breakthrough? Again, it comes back to another difference between Creasy's amendment and Umunna's: the organisational backdrop. The reason why the government knew it had to retreat over abortion is that pro-choice women MPs have honed and shown their organisational power in resisting the increasingly nimble pro-life lobby. And although yesterday's vote came down to numbers, earlier alliances of that cross-party group have come down to persuasion: on why, for example, an amendment notionally sold as limiting sex-selective abortion would de facto limit all abortions.

Remainers in the Commons – not just Labour but Conservative ones as well – are still struggling to organise and exert themselves. Last night's vote couldn't even pull in all the Labour MPs who believe that, as McGovern put it last weekend, "there is no better anti-austerity policy than remaining in the single market". The timing of the move even managed to earn a public rebuke from Unison's general secretary, Dave Prentis, though note that he highlighted that the European question remains an ongoing issue.

There is a deal that keeps Britain in the single market but allows some kind of deal on free movement – it involves remaining subject to the European Court of Justice but not being able to influence it, and paying a larger net contribution to the EU budget than we do now. That deal might be able to command a majority vote in the Commons, albeit only with a large Conservative rebellion, and a great deal of persuasion from Remainer Labour MPs to their more nervous colleagues.

But time is running out for Parliament's Remainers to learn the organisational lessons of pro-choice MPs.