Galleries and dealers hold the records of who owns what. The records are sometimes breached, more often gossiped, and occasionally subpoenaed. A collection a principal believed was private is named in places they did not expect: a dealer's internal database that was shared in a divorce, an auction house consignor list that surfaced in a court filing, a journalist's notes published years after the conversation.
The dealer's interest is in keeping the relationship discreet; the dealer's records are not in the principal's control. A dealer who leaves the trade, sells the firm, or simply changes systems can carry years of consignor information into hands that did not exist when the original purchase was made.
The published auction record is the more permanent half. Major sales are recorded in the catalogues. The catalogues are scanned and made searchable. A lot description that names a consignor (or names them by implication, through the provenance) sits in the record for the life of that record.
The work in this category is largely about awareness. A principal who knows what the trade quietly knows about their collection is in a different position from one who assumes the dealer's discretion is the only thing in play.
Knowing what the record shows is the starting condition for anything sensible that might follow.