Document use of retyped comments for incompatible enums

When upgrading a "enum" type in my contract, I have these cases:

Base enum
enum MyEnum { AA, BB }

• Keep enum size the same but change the names.
  Example: new enum: enum MyEnum { AA, BC }
  This is marked as invalid though it should be valid.
• Shrink enum size.
  Example: new enum: enum MyEnum { AA }
  This is marked as invalid. I "could" be valid
• Grow enum size.
  Example: new enum: enum MyEnum { AA, BB, CC }
  This is marked as valid.

However, I think that being all uint8 internally, there is no incompatible types, and they should all be valid.

No file or test is named. Start by reviewing the upgrade validation documentation and the enum examples in this issue, then document how retyped comments affect unchanged, shrunk, and grown enums; done means each case has clear validity guidance.