Duplicate serial number on different Extreme CF cards

Hi, new to the forum but a long-time SanDisk user. I purchased two 64Gb Extreme CF cards today from a major retailer to use in my DSLR. I register all of my cards with SanDisk so I can keep up with when they were purchased, etc. I registered the first card okay, but when I started entering the registration for the second card I noticed it has the same serial number as the first one. I usually buy only one card at a time so I’ve never noticed it before, but this time I took advantage of a sale and picked up two of them. Has anyone else run into this before? And what can I do to resolve it? Thanks in advance.