AppleCare+ plans must, in most cases, be instigated within 60-days of purchase from new. Coverage then continues for as long as the plan is maintained, ending only when the plan is cancelled or renewal is no longer available.
Cosmetic damage (including minor dents) that does not impact operation of the device is not covered by AppleCare+. Minor dents scratches are considered to be general wear and tear - as expected with natural, gradual deterioration of property, fixtures, or items resulting from normal daily use. By contrast, if a device were to fall from a table onto a hard surface and suffer substantial damage (such as cracked screen or physical buttons ceasing to operate), then a claim under the AppleCare+ plan would be expected to be successful.
If you are unable to determine whether or your device would qualify for replacement under your existing AppleCare_ plan, you would be best advised to visit the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to hands-on assess your iPad - and you can explore your available options:
Genius Bar Reservation and Apple Support Options - Apple