Yes. When someone checks out and you have connected a package to the payment form they checked out on, they will have access to all of the files in that package.

So, for example, when a payer checks out, if the package only contained 1 product, the payer will have access to that 1 product. But, if you add 3 additional products to the package after they check out and they still have access to that package, they’ll have access to download the 3 additional products in it as well.