Hi @ExeterYork, if your DC's potential decision to put U of York as insurance is heavily contingent on the expectation that those insuring are guaranteed accommodation, then I would encourage them to check your assumption with the university first.
The para you refer to states that those who have put U of York as their firm or insurance choice can apply for accommodation as soon as the 2023 entry accommodation portal opens.
Elsewhere it is stated that those firming get priority over those insuring (at the time of the 'great sorting') immediately after A-level results day. In additional, in yet another section, as flagged by @Tree543, it states there is a guarantee for those firming by a specific deadline but does not mention those who have put U of York as their insurance choice.
My interpretation of the confusing info is that, for those happy to put U of York as their insurance option at this stage, there is benefit to doing so soon as they can join the accommodation 'queue' as soon as the 2023 entry accommodation portal opens. At the time of the 'great sorting' they will be behind all those who firmed and stated accommodation preferences by York's cut-off date (usually June) but would be at the top of the list of those who had insured (as, within each category, sorting is by date of applying via the accommodation portal); this is not the same as a guarantee but does improve the odds. However, my reading of the situation may not be correct, that is my overall point!
One of the issues is that of U of York has clearly not updated its text since the 2022 entry cycle apart from some intro paras, adding to the potential confusion. So, your assumption may be correct (which, I agree, would be great) but it might also not be correct, hence my suggestion that your DC clarifies if that aspect is important to them. I hope that helps to some extent!