There is no Event about the Reverse ENS Name changed, it is not convenient for the third-party to monitor the Reverse ENS Name updating information.
This is the tx of a contract first time call setName(string) of ENSReverseRegistrar: https://etherscan.io/tx/0x3999a6c26c827aa5a079c503e81ae6c82c9baaefbbc2af670f1cad98a5ec4a3b
There is two events:
NewOwner (index_topic_1 bytes32 node, index_topic_2 bytes32 label, address owner)
and NewResolver (index_topic_1 bytes32 node, address resolver)
This is the tx of a contract second time call setName(string) of ENSReverseRegistrar: https://etherscan.io/tx/0x036788f6b1e638884fbaee1f3aea2aff84ef34123197c02efa12c33d5877a4f5
There is no events .
I known that a team monitor by setName function of ENSReverseRegistrar(0x084b1c3C81545d370f3634392De611CaaBFf8148), but it will ignore the contract call the setName function of ENSReverseRegistrar.