Normally, where I come from anyway, verifiability would refer to the ability to prove to a classical skeptic that the quantum device did what it's supposed to, cf. e.g. Mahadev (https://arxiv.org/abs/1804.01082), Aaronson (https://arxiv.org/abs/2209.06930), in a strong, theoretical, sense. And that's indeed relevant in the context of proving advantage, as the earlier RCS experiments lacked that ability, so “demonstrating verifiable quantum advantage” would be quite the step forward. That doesn't appear to be what they did at all though. Indeed, the paper appears to barely touch on verifiability at all. And – unlike the press release – it doesn't claim to achieve advantage either; only to indicate “a viable path towards” it.