I thought the Cackle invoice from my recent purchase was pretty straight forward:
Quantity Description Price Each Amount
15 WHITE LEGHORN PULLETS 2.42 36.30
The additional three should integrate fine. Just a friendly suggestion, call your PO the day before and ask them to call you ASAP regardless of time. I called my PO the day before and asked them to call me ASAP regardless of time and they called me at 3:something in the morning- which was fine by me. Considering the invoice is clear when they ship you could always call your PO too. Good luck!