It takes a very long time for decay to appear under a crown if it was done correctlty. If there was decay and they crowned it....their fault. If they weren't properly sealed....their fault! I would not hesitate to address this with the dentist.
If the crowns were done within the year, I'd argue that they were placed when there was current decay underneath them and therefore all decay should be removed and new crowns placed with the cost being absorbed by the dental office where you got them done.
If they have to drill through the crown to remove decay they could seal things up with resin. Even though it's not the best option, it's better than having to pay for new crowns. However, if they have to break the crown completely to get at the decay...yep new crowns would have to be made for you.
In most cases.....a good dentist will make darn sure there is NO decay on the tooth when he's prepping it for a crown and double check the area before cementing it on.
good luck