external Req loaded but later cancelled, how do you get cancellations sync'd?

For those who load Requisitions, POs and Receipts from external source, how do you handle the cancels?

Req_Loader is only for new Reqs, and not Req that gets cancelled within either PSFT or the external source.  So what do you do to keep the 2 systems in-sync?

Same for POs and receipts -- how do you deal with the cancellations?

any thoughts and/or suggestions appreciated!

thanks