renewing account before it expires

Solution 1:

They do stack.

If you have a look at the expiration date for any PS Plus content you've downloaded, you'll see it has been expanded by 1 year exactly.

On PS3, navigate to any PS Plus game, press , select Information, then scroll down to Expires.

On PS4, navigate to any PS Plus game, press OPTIONS, select Information, then scroll down to Valid Period (End) or to Remaining Time.

On PS Vita, touch and hold any PS Plus game, select Information, and see Expires or Remaining Time.

Due to DDoS attacks taking down SEN in December, Sony has decided to gift 5 days of PS Plus to whomever had a valid subscription in 2014-12-25 (December 25 of 2014). Because of that, it is possible the expiration date for your game may have been extended by a year and 5 days.