Multiple Tracking Numbers - What Order?

We have a script that sends our fulfillment email, which adjusts the tracking link according to the ship method and the like. However, when there are multiple shipments on the same order, there seems to be no rhyme or reason as to the order the tracking numbers are listed on the Sales Order.

I talked to NS support (case# 1530631), and they said they thought this was working as designed, but would look into it. I have no idea why listing the tracking numbers in apparently random order would be a design feature, but there you go.

Needless to say, we need to send our customers the correct tracking number. Has anyone else run into this problem? Does anyone know how to get the most recent tracking number from the list? We were using nlapiGetFieldValue('linkedtrackingnumbers') on the sales order, and then splitting those on the space into an array and grabbing the last one, but since 'last' doesn't mean 'most recent' we're running into some real trouble.