Hi Bigboss,
The operational bulletin related to medical extensions has already expired, making extensions obsolete. However assuming that you are still eligible for an extension (rare if your background checks are in progress), medicals can only be extended within 90 days of their expiry for a period of 1 year. If an extension is NOT granted within the 90 days, then it is confirmed you will have to do the medicals again.
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Again assuming you are eligible for a medical extension, you will be getting an email from your VO that your medicals have been extended latest by December. If you do not get this email by then, you can assume for sure that you have to under go medicals again for your immigration to be processed.
Sorry it is not the positive information you were hoping for.
Regards,