I moved this to "My Account Online" as a more appropriate spot.
We have had reports from people who say they've added digital retail subscription cards they purchased online one after the other and simply extended their subscription that way, but that isn't supposed to be how it works. You are supposed to wait until one subscription is nearly over before renewing.
The ultimate answer would come from Customer Service who handle all account matters: Contact Support
Basically as long as the product on that new card is the same as what you've got then it should extend it, you can but try I suppose.
If it's for a different suite you'd have to uninstall/reinstall and the license would go 1 year from whenever you started it.
Thanks for replying.....
Maybe not risk until last week of current sub. (unless see in print can do whenever)
Funnily I was regretting buying an additional pack (on offer last week) until you solved my earlier issue LOL
Probably the wisest thing to do.
Glad to help ;-)