Per this KB question, it appears that the FME Server REST API documentation could do with some updates:
https://knowledge.safe.com/questions/78689/fme-server-rest-api-job-history-limited-to-1000.html
It would be great to see the documentation updated to acknowledge the limit of 1000 job history records per call.
While you're in there, it would be nice if the documentation could also describe the "-1" values for the limit and offset parameters. Although these values are implied by the example given in the API test page, they are not actually documented.
Finally, do the limit/offset values start at 0 or 1?
All of this information can be discovered via trial and error but updated documentation would avoid the need to do this...