Just received this NGC old fatty sample slab with a 1964 D Kennedy. This one isnt shown in sampleslabs.com, although it is close to the 13.2 just has NGC rather than NGR. Also, was it an error to not put the D mintmark on the lable? What do you think @Conder101?
It seems like new varieties have been discovered since the sample slabs website was made. I've also seen a few examples of sample slabs where the mintmark does not match. In this case, they might have just used any 1964 and not distinguished between mint marks. There are even slabs where it has a mint mark on the label but the coin does not (I'd consider those to be slightly more significant although both can be considered "errors").
Cameron Kiefer set up the Sampleslabs.com website something likr 17 years ago. Cameron has been dead for something like 12 to 15 years and it hasn't been updated since he died. In the Sample Slabs book (first edition), your slab appears to be NGC-050-4-6 (Company is NGC, denomination is 50 cents, slab style #4, 6th variation in that denomination/style) One thing that concerns me though is NGC-50-4-6 does not mention the NGC after the date on the label. I don't know if that was an oversight of if this is a different variety (no example is pictured) but the serial number matches. In my book I had this general style listed as NGC 5S (NGC generation 5 sample) but I only listed three variations and I didn't list different denominations separately.