Not true.Technically, there is no limit but they approve a charge based on your ability to pay.
NPSL cards aren't like charge cards. They have a credit limit, it's just not a hard credit limit, like the platinum card would have.
For a standard card, you cannot excede the credit limit. If you try to charge something that will put you over, it will be denied. Full stop.
For an NPSL card, the issuer may allow you to excede the assigned credit limit. Whether you are allowed to do that is totally at the discretion of the issuer, and the decision is usually made on a case-by-case basis. Your ability to pay only has to do with the decision in as much as they'd like to be paid back, like they always do.