Labor did vet every Candidate at the last election, and anyone with an issue renounced any foreign citizenship before the election. This issue is that the foreign government (in these cases, the British Government) had not finalised their end before the election. All advice to Labor was that all “necessary steps” were taken and so there was no issue.
Now in hindsight and with a recent High Court ruling, the Labor position could go either way. To be fair, I do not think you can compare, doing nothing to taking action, as was required of all Labor people. At the end of it all, it is a High Court decision.