I have been given a number of licence keys my company purchased for Acrobat but I don't know the status of each one. How can I tell which key is free?

I've inherited a spreadsheet with a load of licence keys and nothing else, no boxes, no account details, no version details, just keys. They were purchased legit by my predecessor who was awful at logging licence keys and now I need to determine which keys are free to use on other machines. I suspect these keys were once used on laptops that are no longer in use and possibly destroyed. What are my options?

Thanks in advance.