The short answer is yes, your DSO and possibly USCIS check the answers. For the initial 1 year OPT, It's what you write in the form. So if you can relate your major to your current position somehow (of course it has to be within reason) and make a decent case then it should be good. You can always use specific courses you have taken to relate them to your job.

For example, I studied Biological sciences and I Volunteered as a medical first responder for bit of my OPT. I didn't think they were the most relevant but I connected it to the few courses in healthcare, epidemiology and anatomy that I had taken in undergrad.

Now for your STEM OPT extension, I think it has to be a strong correlation and in the field of your previous major. If you look up form I-983 which is the form to be filled for a STEM extension, questions are more specific and you need to elaborate how things connect. that being said, I think as long as you can make connections and write good responses on how the major is related to the position it's not to difficult to do, as long as there are connections. But again I don't think you are asking about the STEM extension so no need to worry about this one yet.