I can think of two approaches.

First come up with a process to test the target for the last date loaded and then use that information to query the source appropriately.

Second build a logging mechanism that records the date(s) used in the last run. Then use that information to adjust your date (range) for the next load. Personally I like the logging approach for a variety of reasons.

--Only one or two rows to query to get your date range instead of an entire table.

--Logging can be useful for a lot of things outside of determining the next date range to use. Audits, results reporting, etc.