@Kris Wood The first Item fulfillment related to a SO would be the one with the lowest internal ID among all of them.

this is probably not safe, netsuite says not to use internal id for create order. Internal IDs Do Not Indicate When Record Was Created

If that is not safe then he should be able to get created date (datecreated) last time I checked that return min and seconds.

I'm using internal ID for the moment and it seems to be working. I'll update it to created date though, thanks!