What is the difference between LastModifiedDate and SystemModstamp, and why does it matter for integrations?

Both are audit timestamps, but they are not updated identically:

1. LastModifiedDate: Reflects changes attributable to a user or a process acting as a user. It is what business users expect to see and what appears on the record.
2. SystemModstamp: Reflects those changes plus system-driven updates that Salesforce applies internally without touching LastModifiedDate.
3. Why it matters: A delta integration that bookmarks on LastModifiedDate can silently miss records that were changed by the system. SystemModstamp is the safer high-water mark, and it is indexed.
4. The other half of delta design: Neither timestamp tells you about deletions. Use queryAll and getDeleted, or Change Data Capture, so that deletes propagate. Also overlap the window slightly and design the target to be idempotent, because clock boundaries and long-running transactions will otherwise drop records at the edges.