Exchange Server TLS guidance Part 2: Enabling TLS 1.2 and Identifying Clients Not Using It

The_Exchange_Team we have TLS 1.2 registry [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\SecurityProviders\SCHANNEL\Protocols\TLS 1.2 turned on our 4 Exchange onprem servers - We DONT have a client registry entry. All four Exchange servers are configured for hybrid communication to our Exchange Online environment. Mailboxes on 3 of the 4 Exchange  servers can retrieve Free/Busy information from EXO env,  but mailboxes on a single server with same registry config can not see EXO free/busy. Free/Busy from Exonprem is available to all EXO mailboxes regardless of server. Test environment when configuring TLS registry keys to include Client key seemingly resolve issue. Is there an explanation as to why 3 servers without Client registry entry can retrieve Free\busy from Exo without Client TlS registry key existing?