When Migration Assistant (or Setup Assistant) migrates Keychains, it successfully transfers most items as expected, but behaves (very) strangely with respect to the "Local Items" keychain. It appears, rather than transferring the current contents of "Local Items", to create a new set of items (at least partially) from old entries in the "Login" keychain, resulting in many items on the target machine that are missing or out of date.
What is the logic behind this behavior — is it a bug? (and is there a way to recover the correct contents of the source machine's "Local Items" keychain)?
I'm aware that the "Local Items" keychain is not really a keychain, but a database inside a folder named for the GUID of the machine where it is "Local". But this only deepens the mystery, since this folder is completely transferred from the source machine, but seems to be unused by the target machine and inaccessible there from within Keychain Access.