In the assets tab, for a few assets, you see a differrent 'created on' date which seems different from the date on which the DCS agent was actually installed on the asset
By Design
The time seen in asset creation date is the date/time on which the asset was registered with the management server & not necessarily the agent installation date.
There are may reasons/situations in which the agent installation time may vary from the registration time; If such a situation arises, the creation time on the UMC will differ from the agent installation time.
A few examples would be - the agent was only installed earlier & registered later on, the agent was registered with a different environment / management server earlier, the agent was re-registered later etc.