Getting back to the topic, different organisations have different requirements as to when insignia or titles need to be updated.
For example, all QCs became KCs as soon as Charles took over, so all the business cards and letterhead had to be binned.
Post boxes stay pretty much forever and only get a royal insignia when replaced. Hence you see Edwardian and Georgian post boxes. The vans will probably get done when they are due for a respray (if Royal Mail is still going - it's not just the workers, they have a hefty payout to give to all the postmasters that they shafted thanks to their IT system).