Hi, @John Bigg
Here is a User Voice about the same issue for your reference:
https://configurationmanager.uservoice.com/forums/300492-ideas/suggestions/34820848-i-have-a-suggestion-for-the-smsslp-parameter-and-r
And a similar thread in TechNet forum:
https://social.technet.microsoft.com/Forums/en-US/d77ff560-cfe1-403a-b0b7-b849d358b1f5/quotsmsslpquot-registry-key-shows-old-sccm-server-name?forum=configmanagerdeployment