While SCCM admins plan to upgrade sms client to sccm client and you have a large SCCM infrastructure with multiple sites, make sure that you have configured site code within client push installation method of primary sites or if you have planned to upgrade clients with software distribution methods, don't use auto discovery for all clients, it can cause you a large no of unhealthy clients. You will see number of clients which have client installed but showing as 'No' to sccm console. To eliminate this, you can prepare site wise client upgrade package and can deploy it to respective sites.
One more good option is to prepare a script which will discover client's site boundary (AD site) and assign site code immediately. this script can be deploy to all clients within your sccm infrastructure centrally.
Anyway, if you have such computers in which client is installed but showing 'No' in console, one more option is to set the correct site code and resolve the issue.
Hope it helps.