The model number is on the bottom of the box and is the key to your issues. It usually is on the invoice as well so there is no need to be concerned.
Model numbers
You can see the model number in Settings, General, About, Model. The model number has a two-letter code, a number and some more letters. The last part stands for the country/region[1]. The first letter can be "F" (refurbished), "M" (normal retail), or "P" (personalized / engraved). For example MC605B is the model MC605 and B is for the region[1].*It is also on the bottom of the sealed box so just find out what model(s) iPad you want and then you can verify it just by looking at the box. This apples to any product.
iPad 3 – Black
MC705ZP/A - iPad 3 Wi-Fi only 16GB - Black
MC706ZP/A - iPad 3 Wi-Fi only 32GB - Black
MC707ZP/A - iPad 3 Wi-Fi only 64GB - Black
MD366ZP/A - iPad 3 Wi-Fi + 4G 16GB - Black
MD367ZP/A - iPad 3 Wi-Fi + 4G 32GB - Black
MD368ZP/A - iPad 3 Wi-Fi + 4G 64GB - Black
iPad 3 – White
MD328ZP/A - iPad 3 Wi-Fi only 16GB - White
MD329ZP/A - iPad 3 Wi-Fi only 32GB - White
MD330ZP/A - iPad 3 Wi-Fi only 64GB - White
MD369ZP/A - iPad 3 Wi-Fi + 4G 16GB - White
MD370ZP/A - iPad 3 Wi-Fi + 4G 32GB - White
MD371ZmP/A - iPad 3 Wi-Fi + 4G 64GB - White
Below is a link to the complete list of model numbers. Ignor everything except the right hand product code.
Please note this list is USA only and does not reflect the several region models for iPad 4 th generation 4g and ipad min 4g. In saying that the wifi codes will be the same expect the region number will change. Hope that helps.
http://theiphonewiki.com/wiki/index.php?title=Models