A 2015 customer-history review covered eighty-four thousand number disconnections. Fifty-one thousand numbers were reassigned during the review year. An analytical join used the telephone number as though it identified the same customer throughout the period, bringing records from an earlier assignment into a later one. The field was convenient and widely available, which made the mistake easy to repeat across apparently consistent extracts.
The analytical sponsor preferred a continuous history because it made longer comparisons possible. I asked for the assignment evidence before accepting that continuity. A telephone number could identify the service within an interval without establishing that two intervals belonged to one person. We gave up the convenience of a single uninterrupted number-based account where the source did not justify it.
S$2.4 million funded the data response. The team retained assignment intervals and connected records within the supported relationship, preserving the disconnection and reassignment evidence used to distinguish them. Where timing or identity remained unresolved, the uncertainty stayed visible. We did not claim that every disconnection led to a new person or that every reused number established an entirely unrelated household; the review supported boundaries in the account, not speculation about identities beyond it.
Privacy and legal owners assessed permitted uses of customer information. The data correction did not itself confer permission to combine records, establish anonymisation or settle a person’s rights. No actual subscriber details appear in this fictional example. The delivered change was a more faithful relationship between a number and its dated assignments, with unsupported continuity removed from the analytical view.
I would include reassignment scenarios in the original requirements for any customer-history product. Testing only stable numbers had allowed an easy identifier to stand in for a difficult relationship. The important enterprise change was that the history now required evidence of continuity rather than assuming it from a familiar field. That made some analyses shorter, but made their claim about whose experience they represented more defensible.