Possible Model Number Issue?

[kamakazi]

I was going through my collection of Atari 5200 games, taking notes on variations in labeling, and I noticed something rather odd. So I visited the handy-dandy AtariAge 5200 database for some research. The game in question is Defender. I purchased the game used from Atari2600 complete in box but not everything matches. The cartridge and box use the dull gray and carry the Atari Corp. copyright. They also give the 5218 model number. Then here comes the instructions that were printed when Atari was under Warner Communications. Atari, Inc. is the copyright as expected but the model number given is 5211. At some point did Jack get the numbers mixed up? Or maybe he decided to change them around? 5211 should belong to Dig Dug. Does anyone have an Atari Inc copy of Defender where the model number can be confirmed for me please? Thanks.