A sanctions list is a state of the world, republished in full each time it changes. There is no feed of events. Anyone who tells you that a particular entry was added on a particular day has either read an announcement or compared two files.
Snapshots
Each time a list is retrieved, the whole published file is stored with two dates: the date the authority says it published it, and the time we fetched it. That stored file is a snapshot.
Snapshots are what make the section reproducible. A question about someone's status is answerable only in the form "according to the version published on this date", and without the stored version there is nothing to point at.
Comparison, and why it must be complete
An entry present in one snapshot and absent from the next has been removed. An entry present in the second but not the first has been added. That comparison is the whole mechanism.
It has one catastrophic failure mode. If a download is interrupted halfway and the partial file is treated as a snapshot, the comparison reports that half the list was removed — thousands of false statements about the legal status of real people. For that reason only snapshots recorded as complete are ever compared, and an aborted retrieval is discarded rather than stored.
What a derived change does and does not tell you
A derived addition means the entry appeared between two publications we hold. If the authority published three times and we captured two of those, an entry that came and went in between is invisible.
The date of a change is therefore bounded, not exact: it happened somewhere between the two publication dates, and both are shown. We do not present the date we noticed something as the date it happened.
Amendments are not additions
Entries are edited in place. An address is corrected, an alias is added, a programme code changes. The entry was not newly designated; its record was updated. Comparing only names would report such an edit as a removal plus an addition, which would be two false events.
Matching is done on the authority's own identifier for the entry, which is the only thing stable across edits.