[RANT]
I was right! Of course they never expected anyone to need more than 99 entries for a purchase order. I guess no one out there has more than 100 items that may not come in at the same time, right? (read: save the PO more than 99 times)

And there are "currently no plans to increase the field size to 3" according to them.
So, we get to recreate the POs in smaller chunks, and start over. No telling what inventory nightmares those errors are going to cause.
You have been warned!
[/RANT]