1) Expiry date is not mentioned , but IRCC considers for 1 year . Lets say you took ur tests and submitted on 1st JAN so its valid upto dec31 . And if with genral trend your application gets processed in 6months (since AOR ) lets say your AOR is 1feb so if they approve your application at anytime they give you time to enter canada before dec31 ( thats based on your medical 1year )
2) If you have already applied and in middle the medicals expired lets say , your application took longer than regular by any means .. They send you the notification and the medical centre will receive re-test remark on your e-medical acknowledgement . For which they charge fee just as new medicals .