This is true for all public holidays in the UK, there’s a (usually) fixed number of public holidays but the dates are flexible.
They’re also included in the minimum 28 days paid time off too, meaning if you’re a full time worker and have to work on a bank holiday your employer is legally required to offer an extra day off somewhere else instead, either a fixed date or added to your holiday allowance. Conversely, the “extra” day off you get when a monarch keels over may be subtracted from your holiday allowance for the year. This is also why my employer is allowed to follow English bank holidays despite having next to no presence in England; the number is fixed but the dates are not.
Why bother? They’re safe at room temperature unless they’ve already been refrigerated, might as well use that fridge space for some that actually benefits from the cold.
At room temperature they’re good for a month or two. If you want long term storage you might as well prep and freeze them which will last you about a year, or there’s a ton of other long-term preservation techniques.