There don’t seem to be any specification updates or errata lists for any Intel 486 CPU anywhere. It’s odd because there are specification updates for 386s (and of course Pentiums) from Intel, and because the embedded 486s continued to be produced for a long long time (standard 486s well into the 2000s).
The 486 was released back when Intel believed that publishing errata would be damaging and it seems the policy was never changed, as it had been for the Pentium (after the infamous FDIV fiasco).
Someone, somewhere has the errata sheets. Anyone want to share?
The reason this is interesting is because a quick look at an early production 486 (S-spec SX308, late 1989/early 1990) revealed quite unexpected results when running a utility from Undocumented PC testing undocumented instructions. On this 486, two undocumented alternative TEST encodings were missing. Every newer 486, just like every 386, Pentium, up to current Core processors supports these. What else did the old 486s do differently? The poorly chosen initial CMPXCHG encoding is well known and inverse CR0 bit semantics are documented in Intel’s original datasheet, but those do not apply to the SX308 S-spec.
Related fun fact: Intel announced the 486 in April 1989 with 25 and 33 MHz speeds. Some take it to mean that these were actually available in 1989. Reading contemporary reports (c’t Magazin) reveals that the 25 MHz variant was very close to unavailable before 1990 and the 33 MHz version didn’t even exist.