If First Install Date is the same as the saved date, the CPU was probably not changed. Check the Install and First Install Dates, and compare them to the one you saved. You'll see an entry for each core and thread your CPU has. Now find Processors and double click that. If the two dates are the same, you have a better chance. If Install date is later than First Install Date, the OS was reinstalled at least once, and your chances of checking if the CPU was replaced are less. If Install Date is the same as First Install date, then the OS has not been reinstalled at on the PC. If the First Install date seems reasonable, such as about as old as the PC is, then write that date down, and you can continue. Click on Device Description and look for 'First Install Date', and 'Install Date'. Double click that to open it's Properties, and click the Details tab. Under Computer, you should see an entry like 'ACPI X64-based PC'. Open the 'device tree' by double clicking on the first entry if it is not already open. Start Control Panel, and then Device Manager. But my mother board saved the First Install Date, which is not the same as the Install date, and maybe yours does too, you'll need to check that. I've re-installed the OS a few times, so Install Date and First Install Date are the same for almost everything on that PC, and is the date I last installed an OS, 2012. The Install Date always changes whenever a OS is installed, including being installed again. Most devices don't, but some mother boards do, and the PC I'm using now does, it was first used by me and had it's first OS installed in 2009. The First Install dates are created by Windows when it is installed, unless the device provides (really saves) a date. The dates you will be looking at are Install Date, and First Install Date. It's not perfect and exact, but if you're lucky, you might be able to tell. You might be able to check if the CPU was replaced by it's install date, but that depends on the mother board, when the Operating System (Windows, etc) was installed, and if the OS has been installed more than once on the PC.

Check windows install date