For books we look at three things: the page layout and its column count, the publisher's block and prefaces for a date, and the seals and marginal notes of former owners. For letters, identity comes first, and it needs at least one corroborating fact — another letter of the same period, the dedication, or a record of the recipient.
Holders of a whole family lot may send an inventory first: we value it as a group, so nothing has to be submitted piece by piece.
