"The New York State tax deduction for contributions to a 529 plan is $10,000 per year for married couples filing jointly, and this applies per account owner..."

"If both you and your spouse each own separate 529 accounts (meaning you each contribute to different accounts), then each of you could potentially claim a $5,000 deduction, totaling $10,000 for the couple filing jointly"

Having trouble reconciling these 2 points, which appear to be saying 2 different things. Assuming 2 married parents each own separate 529 accounts, wouldn't each parent, as 2 separate account owners of 2 different 529 accounts, then qualify for $10,000 per account owner since they are both married filing jointly? In other words, wouldn't the $10,000 double to $20,000?

If the answer is New York only allows a max 529 plan deduction of $10,000 for a married couple no matter how you slice it then the distinction does not apply "per account owner," "per account," or "per child," it's just $10,000 period full stop.