The answer to this is that they do not. They are Land Registry documents required to remove the reference to the charge from the relevant registered title. Panel 6 in form DS1 is drafted as follows:-
“The lender acknowledges that the property identified in panel 2 is no longer charged as security for the payment of sums due under the charge”
The phrasing of the form makes it clear that the form can only be completed once the charge has actually been released. However, in a recent case Garwood The Bank of Scotland PLC  EWHC 415 (Ch) the court considered that filing a form DS1 can operate as both evidence of discharge and an application to alter the register. In that case, the charge was considered capable of reinstatement on the title on the grounds that form DS1 had been submitted due to a “mistake”.
Here are some practical points which follow from this:-