CRB checks show the date on which they are printed but they do not carry a pre-determined period of validity.  This would be impossible to police as a conviction or matter which could be raised in the event of a CRB check being completed, could be recorded against the subject of a CRB check any time after the initial CRB check has been issued.

It is standard practice for new CRB checks to be carried out by each setting in which a subject of the a CRB check is working or volunteering.  At least this way, they are ensuring for themselves that they have the latest data at the time of taking the check.