You have searched and compared many off-white paint colors for your walls, ceiling or trim. Of the 150+ off-whites to choose from you have narrowed it down to Navajo White, or maybe antique white. But who's Navajo White?
Navajo White chips in Sherwin Williams, Pittsburgh Paint and Benjamin Moore
The same color name does not mean the paint color will be the same!
You may have stopped into a couple of stores to get paint chips, but your painter has told you about the benefits of the specialty paints and / or you always use a particular paint, like Benjamin Moore products. Based on the color you chose, it could be another company's color that you want mixed in your preferred paint. For example you stopped into Lowe's and picked up an off-white paint chip that just really works in your room compared to the other off-white chips. There's just something about the color you like it best. From your research you know you want to buy paint from your local Benjamin Moore owner instead of using the products offered at a big box or commercial store.
I strongly recommend to have the paint chip with the person placing the paint order and to clarify the details as to the brand and sheen of paint being used on the space. Ideally you want to get a paint color made by the company you are getting the paint mixed in, but it isn't a perfect world and sometimes you just really like a certain color for a certain reason. All is good. If you go with the cross over of color and product, just have the store open the can and make sure the color is close. If it is a non-company color it will never be 'exact', but it shouldn't be noticeably different either.