Old debt does not simply expire. What expires is the window in which a creditor can enforce it through the courts, and that window can be reopened by an action the borrower may not recognise as significant.
What a limitation period governs
A limitation period sets how long a creditor has to bring a claim. Once it has passed, the debt is usually described as time-barred.
Time-barred is not the same as cancelled. The obligation still exists as a matter of record, and the creditor may still ask for payment.
What changes is the enforcement route. Without a viable claim, the creditor loses the ability to obtain a judgment and everything that follows from one.
Why the start date is often disputed
The clock generally runs from a defined trigger, commonly the last payment or the point at which the account fell into default. Identifying that date precisely is where most disagreements begin.
Records are imperfect, particularly on accounts that have changed hands. A buyer may hold a default date that differs from the one the original lender recorded.
Because the start date determines whether a claim is viable, it is frequently the single most contested fact in an old-debt dispute.
How a payment restarts the clock
In many jurisdictions, a part payment or a written acknowledgement that the debt is owed resets the limitation period to zero. The size of the payment is usually irrelevant.
This is why collectors on aged accounts sometimes press for a token amount. A small gesture intended to show good faith can restore an enforcement route that had lapsed.
Acknowledgement can also occur in writing without any money moving, depending on local rules about what counts as an admission.
Why time-barred debt still gets collected
Nothing prevents a creditor from contacting someone about a debt that can no longer be sued on, provided the contact itself is lawful and not misleading.
Aged portfolios are cheap precisely because enforcement is weak, so the business model depends on voluntary payment rather than legal pressure.
Some jurisdictions require the collector to disclose that a debt is time-barred; others do not. That variation explains why the same letter would be compliant in one place and not another.
Where jurisdiction changes the answer
Limitation periods differ by country, by state or province, and often by the type of agreement involved. Written contracts, oral agreements and judgments are frequently treated differently.
Rules on what restarts the clock vary just as widely, and they are amended over time. A rule that applied when an account defaulted may not be the rule that applies now.
Anyone dealing with a genuinely old account is in territory where the general shape is predictable but the details are not, which is the point at which local advice becomes worth the cost.