Correct. So basically if you gave your medical before entering Canada earlier (Study or Work), you can use the older one and the visa officer will check for your travel records, if you have been in Canada since your last medical then the old medical will suffice. If you have travelled to other country/s during that period, a new medical will most likely be requested by the officer.but on website it doesnt mention about the particular time period and i have seen a post from a person on fb he passed his medical from 2018 year.