A service contract covers a specific unit, and the contract identifies that unit by something: a serial number, a model and serial pair, or an identification number printed on the unit. That identifier is what ties the contract to the thing it covers. If the identifier stops matching the unit in front of you, the cover can be disputed even when the contract is in force.
Where the identifier lives
Copy the identifier from the contract, the label on the unit, and the sales paper, then compare all three. Photograph the label and keep the photograph with the contract copy. If someone else delivered or installed the unit, keep that paper in the same file.
When the identifier changes
Part swaps, board replacements, and some repairs can change the identifier printed on a unit. Before a repair that replaces a labeled component, ask the provider whether the contract requires the new identifier to be recorded, and how. Ask whether the contract treats an altered, missing, or unreadable identifier as grounds to refuse a claim, and where in the contract that appears.
When the unit changes hands
A transfer moves the contract to a new owner, and the identifier has to move with it. Send the identifier in writing with the transfer request, and ask the provider to confirm the unit it has on file. Where a state sets transfer rules, the state page names the statute or program, and where a state publishes a roster, the state page prints it so you can match the seller name on the paper to the entry. This guide has not read every state's transfer rule, so check the statute before you rely on any step described here.
What to keep
Keep the contract, the identifier record, any transfer confirmation, and every repair record that names the unit together in one file. When a claim asks which unit was covered and when, that file is the record you will need.