If they are using different generators then how do different interpreters know which generator has been used to decrypt the QR to give an address ? Wouldn't different generators have different address for both QR codes ?
No, QR code is defined such that you can encode your information differently, but decoding will always result in the same information that you encoded (and the decoder will know how you encoded stuff, because that's part of the encoding).
For example, you may specify different amount of error correction info, so the total number of bits (small squares) in the QR code is different, but the actual encoded info is the same.
This is especially useful when you intend the QR code to be printed out on paper that may become dirty or slightly damaged. For display on a computer screen, you don't need to add much error correction.
QR is a pretty slick invention :-)
Onkel Paul