Intel claimed the bug was due to an error in a script to download the entries into the PLA. But due to the 16 missing entries, I think they made a mathematical error in constructing the table, misjudging the effect of a 7-bit adder. Here's the adder, just above the PLA. 6/9
You'd expect that Intel fixed the problem by adding the 5 missing entries. Instead, they filled *all* the unused entries with 2's. This made the table easier to store in a PLA, shrinking it by 1/3. The fixed PLA has lots of unused rows at the bottom. 7/9