Only fetch publications newer than the previous run, and flag sectors seen before as a change signal. Ideal for scheduled monitoring. Uses a shared, persistent key-value store snapshot ('nl-cao-wijzigingen-database-snapshot') that is also read and updated by scheduled monitoring runs, not just this one. On the very first call ever (no snapshot exists yet), there is no previous run date or seen-sectors list to compare against: it falls back to the 'publishedAfter' filter (or fetches without a date filter if that is also empty), and no publication is flagged as a change signal since nothing is known as 'seen before' yet.