> My take is that identity doesn't imply mutability, if you version objects. It could well be that your are looking at an old version of an object, using its unique identity combined with its version (number).

Are you storing the version as part of the object? If so, they’re no longer equal values regardless of identity. If not, what purpose is there in versioning the same value? Even if there is a purpose, are same-value-different-version objects not otherwise interchangeable unless/until some value change does occur?