The COA is designed to assure the end user that the software program is not counterfeit. The COA contains anti-counterfeiting devices, such as a latent image, to prevent the production of counterfeit Microsoft products. I just bought a PC that came with Windows operating system software. The number on the bottom of the COA helps Microsoft and its OEM vendors track legitimate product in the marketplace. Your product serial number is the number that first appears on your computer screen when you turn on your computer.
Concurrent use is the sharing of software licenses among multiple users.
The EULA permits you to store a copy of the software on a storage device used as a network file server for the purpose of installing the software on computers connected to that storage device via your internal network. In addition, you may install the software on a storage device used as a network applications server so that computers connected to that storage device via your internal network can run the software from that source. You must acquire and dedicate a license for each separate computer on which the software is installed and for each computer that runs the software from the storage device. By dedicating a license to a particular computer, you are assigning the license exclusively to that computer for an indefinite period of time. A license to use a particular copy of the software may not be shared or used concurrently on different computers.