Abcd, I respectfully disagree with Don...........
Totally putting market value aside for now - there is a bigger issue - disclosure...........If you want to make sure your home's assessment is accurate because you are selling your home ...then , assuming your contractor got the necessary permits, the town is aware of this, and as Brian siad, it must may be a timing issue until they catch up with you.
So, based on that, I'd call the town and made sure you are scheduled for a final inspection. You can find out when they will come back to inspect the work that was done...and make the proper adjustment in the tax records.
In my opinion, not doing this is cheating the town of the higher taxes that will rightfully be due them - afterall, you put on 2 bedrooms and a bath - that's a huge improvement.......not to mention it will be misleading to the buyer to think their taxes are proper. It's something that could come back to haunt you in the future.
I don't understand how any licensed Realtor can advise you to try and sell your home, knowing full well your taxes are inaccurate.....and not at least disclose this to a buyer, or attempt to make things right. No one likes to pay higher taxes, but you knew your assessment would increase when you decided to make the improvements.
If this is not done in time for you to sell your home., then you should at least disclose it to a potential buyer. (actually, it is part of our seller disclosure forms) . Let them know you made the recent improvements, and are awaiting final inspection from the town, and that the taxes will be increased.................you would never want them to buy the home with the lower taxes, and not be aware that those numbers will change due to the addtion you put on. Not to mention, if the contractor got the proper permits - there is a record of that with the town. I don't think you will have very happy buyers if they find out, after the fact, that their taxes were going up and no one informed them of that. I don't want to be too dramatic, but if the buyers find out after they move in that final inspections weren't done, and no one disclosed this,........you might be accused of consumer fraud. This goes to disclosure.
Do the right thing.....call the town, and let them know the work was completed.........and you are ready for the final inspections ..and dlsclose this openly to any buyers.
One other thing no one mentioned - - you want to make sure the town agrees that the additon was done properly NOW.......not after you sell.