Version differences
I checked the site noginoypi pointed and the EAD cards that we have. The current EAD card sent directly from NSC is called Form 766 Rev 1/3/96. All our cards received from NSC, with the latest being earlier this month, have this form number at the back.
However, last year we had to get an interim EAD card from the local office since NSC had delayed the case for 90 days. The interim EAD card issued by the local office is called Form I-688B Rev 89. This is a plastic laminated card. and looks like the one in that Web Site noginoypi pointed out. Form I-688B Rev 89 is printed on the lamination, in red. This card does not have the enhanced security features of Form 766 such as the magnetic strip, bar code etc., on the reverse.
I am not too familiar with family based I-485 applications, but my assumption is that the person who put up that website had gone the FB route and had all his applications sent to a local office, instead of a service center such as NSC. In that case, his EAD would be I-688B. I guess you have to convince that 766 is the newer version of I688B, and both are the same to that organization.