Screw you, now your calling me a liar?
The reason they can start the dros now and not before is because they actually have the lowers in the wearhouse. When you put your deposit they didn't, therefore they weren't sure if they where going to get them within the 30 day mark. Also, they don't need the serial number to start the paperwork on long guns.
For you, I would suggest you call the store around the 30th of January so you can make sure you will be the last to get one.