It's not just Sams Club, this has been happening for a looooong time in Walmart and other locations. They are covering their buts for lawsuits and people that are printing copyright photos without the photogs permission.
I feel if you have the file, you probably have the pros permission.
I went there about a couple of months ago to make baby announcements for a relative and when I went to pay and pickup, they told me I needed a release as the pictures looked 'pro'. I told them thank you - I was the photographer who took the pictures. She made me sign some form that basically said they were my files and that I took responsibility for making them - something like that, I didn't really take the time to read the whole thing, it's to protect them, not us.
I give my clients a form letter when that's included in the package that says I give them the rights or permissions to make reprints. I have not heard from any clients that this has not been acceptable to any labs as of yet.
I believe on-line labs - it's just a free for all, no questions asked.
suse