Hi sanvik
While you submitted the form 815, then the medical process is finished and you will receive the grant letter from your CO. The letter will explain you for the date of first entry, your visa number and the validity of your visa date and year.
If you are not received yet the grant letter , just remainder your CO by mail will help you to get your grant letter soon.
The last date of your first entry is starts from your first date of medical examination by a year