there doesn't have to be a seam at all corners: I have installed jobs before in an l shaped kitchen where their entire countertop was a single piece. My best guess is that while fabricating a piece of the stone broke and they did the best they could with what remains of the stone.

If they agreed in writing that there would only be one seam, after you specifically asked for that as a condition of sale, then the only reason why you should care why they put in an extra seam is so you can know whether you have the option of demanding they remake it instead of rejecting it entirely.

They are the subcontractor for the Home Depot. So the Home Depot has our money and the sub won't budge and our kitchen is torn up. I am convinced after much research that the seam is not needed. I had one company suggest it probably has two seams because otherwise they'd need to bring more than two installers.

.....Home Depot. No need to go any further. Stop dealing with the sub...and go back to HD and make the complaint. The sub will loose money because of the seams so they don't want to deal with it. Your contract is with HD.

Just to be clear: HD doesn't do well with phone calls NOR emails. They respond very well IN PERSON. You may have to show up on their door step multiple times PER WEEK to get this dealt with.

Many people have had to go toe to toe with HD (hundreds of thousands of people...so lots and lots) and they have always gotten a positive result...but it has to be done IN PERSON...and you have to be persistent for weeks/months.

Good luck. HD will probably deal with it...but it will take up much of your free time for the next few weeks (possibly months). Let us know how it goes. We've watched these HD train wrecks before.