How to check if my macbook IOS is a clean install or updated from an old version

Hi Folks,

I have taken my 2012 macbook pro to a store to upgrade the hard drive to 1 TB solid drive and add more ram (16 gb). I decided to do this upgrade because since I updated from IOS Sierra (10.12) to Catalina (10.15) the computer started to work really slow, to a point that it was very difficult to just use it for internet browsing or any activity whatsoever. Tthe computer is 2012, so I can't update any further than 10.15 Catalina.

When I went to the shop today to pick up my mac, I found it that the tech guy installed El capitan (10.11) I told him I wanted the latest possible IOS which is Catalina. He admited that he made a mistake and promissed me format the hard drive and do a full clean install of Catalina.

I just don't trust he'll do a CLEAN install, and instead he'll just update it.

Is there a way I can check if the IOS is a clean install or just u updated from a previous version?

MANY THANKS GUYS. I really appreciate your knowledge and experience on this.
Regards

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