Don't think I quite agree with that. Norway +, in the form of 'Common Market II', came about as close as anything last year to winning the support of parliament. If Labour had advocated that from the start, it might have found some tough going initially, but May's deal would still have failed in just the way it did, and then Labour would have been left in a vastly improved position.
I say the above partly with the benefit of hindsight, but there was always a strong moral case for something akin to Norway + - 'leave the EU but stay in EFTA' reflects a referendum split nearly 50:50 with no detail of what any brexit might look like much more accurately than any other form of brexit.
imo Labour made the biggest mistake tactically by going along with May's assertion that the referendum result demanded new immigration controls (these are also new emigration controls, of course, something that is all too rarely pointed out). It didn't. Immigration wasn't on the ballot paper. Ed Milliband made the same mistake in bowing to tory pressure to bang on about immigration. Concede that this is a source of the UK's social ills and you already concede a great deal more on all kinds of areas to the right.
Still might not have worked, of course, but it might have avoided the ludicrous situation in which Labour contrived to find itself the party hardest hit by the mess of brexit, a mess created entirely by the Tory party.