Yup oh u March 2021, then surely very soon dear don't even worry at all. Its very clear and easy to predict for the new cases as it looks like they don't waste time to create backlogs at all. Cos u already done with medicals. I am a July 2020 and was given MR July 2021, you can imagine took a year for medical request. From what I see on my file I think within September, October anyway is in God's hands now. Don't even care, just expecting to see some good news as it calms the mind down to know they are working atleast.
Your Prearrival wud come atleast 3 months from your medicals expect it soon dear.