H1-B Petition Granted for 3 vs Expected 1.75 years

[confusedimmigrant88]

I recently got approved for an H1-B visa transfer from a STEM OPT status. I had previously worked on H1-B status in the US, then gone back to business school and graduated to work on STEM OPT and now just transferred back to take advantage of the remaining time I have left on H1-B. I was approved for a 3-year petition (even though I thought I only had 1.75 years left). I communicated that to my company's legal team who is now saying that we they will either have to let USCIC correct their own mistake or contact them to let them know. Is that really necessary? What would the risk be if they did not contact USCIS and I just kept the 3-year petition? Would I have 3-year work authorization status in the US?