Letters patent are a legal document created by the B.C. government. Incorporating letters patent establish the framework by which a municipality or regional district is created.
Letters patent are often considered the constituting documents of a local government, setting out its boundaries, name, and other specific matters.
Letters patent are issued when a local government is created (incorporated) or when something included in letters patent is amended, such as the boundary. Letters patent are typically tailored to a local government’s needs, and they can only provide a local government with authorities available in statutes.
(Taken from https://www2.gov.bc.ca/gov/content/governments/local-governments/facts-framework/legislative-framework/letters-patent)
It should be noted that, as of Ministerial Order 10/2023, Improvement Districts no longer have restrictions on dates for AGMs. This order overrides the 1979 amendment. That Ministerial Order can be found online here: https://www.bclaws.gov.bc.ca/civix/document/id/mo/mo/m0010_2023?bcgovtm=BCV_N4.