Landlord's enduring delay losing current legal document (7,6)

I haven't cracked this one yet — but the brilliant team at Times for the Times have:

LETTER’S + PATIENT (enduring delay) minus I. A type of legal instrument in the form of a published written order issued by a monarch, president or other head of state. Interestingly (to me) the opposite of letters patent are “letters close” which are personal in nature and sealed so only the recipient can read their contents. In 35 years of being a lawyer never heard of the latter and never came across the former.