Matching delivery schedule lines in PO between MM-SUS and ECC

Hi All,

We are trying to match up the delivery schedule lines in a PO line between SUS and ECC. The problem is that schedule line numbers aren't passed to SUS, and SUS sorts the delivery lines in chronological order and sends them back this way.

Take the below screenshot for example:

If I confirm the PO as-is, there's no problem, but if I change one of the dates in SUS, then the return lines are renumbered. 9/9/2016 becomes line 1, 9/26/2016 becomes line 5, etc. Here's the EKES table after I changed the last date in SUS

Our actual requirement is to put the delivery dates coming from SUS into a Z-field, but that field needs to match the corresponding schedule line. Has anyone ever dealt with a scenario like this?

Thanks,
Seth