diplomatics
The science of authenticating, dating, and interpreting old official documents.
countable, uncountable
Paleography might teach men to read documents, diplomatics to date them and to test their authenticity; but the full significance of an ancient deed might easily escape the most exact paleographer and the most accomplished diplomatist, for the want of that finished sense for legal technicality which is the natural fruit of a conveyancing practice.
Where it comes from
Probably from Italian or Ecclesiastical Latin diplomatica.
Adapted from the Wiktionary entry diplomatics (CC BY-SA 4.0).