Time scale for review
It is important not to underestimate how quickly things can change in your organisation so making sure the plan is up to date needs to be a requirement in the standard. Evidence of staff training is important too.
Why the contribution is important
Revising the disaster plan is one of those things we intend to do annually but how many of us actually do? Having a prescriptive requirement in the standard might make sure this important thing is done.
The example of the rise in the water table seems a bit extreme, far more likely that your staff have changed or your organisation has moved insurance provider or reorganised its risk management team (without telling you).
Its not just the archive staff that need training but any other staff that you may have to call on to help you and even if your staff haven't changed the building supervisors might have.