Interesting read. But given the <i>many</i> possible causes:<p><pre><code> # IC degraded due to being manufactured looong ago (~35y+)
# Bad manufacturing batch
# Storage conditions
# Chip at some point pulled from other systems/boards? (which had previous owners)
# Fake chips
# ESD damage
</code></pre>
I'd say "one or more of the above" is more likely than "AY-3-8913 chip has a bug". Or in other words: (probably) nothing to see here.