A debt collector has the specific option under the FDCPA to bring legal action in either the state the contract establishing the debt was signed, or in the state of current residence of the consumer. Should they bring legal action, the prevailing SOL at trial will be that of the jurisdiction in which the legal action is being heard.
SOL is not universally the date of first cause of action, which is usually the same as the DOFD. Some states provide reset provisions.
They may be hedging jurisdiction, and the date of last payment may, in their minds, be significant.
Send them (the current owner, and thus the heir to responsibility to maintain accuracy of the reporting on the accout) a direct dispute, to which they will be required to respond within 30 days by either verifying the accuracy of the reported date, correcting the reporting, or deleting the disputed reporting
They do not have to provide any evidence when verifying. It becomes their legal representation that they have conducted a reasonable investigation of the accuracy, and have basis to confirm its accuracy.
If legal action is brought, it will be part of the court determination of whether SOL applies to determine, if their state statute provides for reset based on payment, whether their evidence is accurate.