Personally I don't think it's anything to be concerned about, but your suspicion that something might be wrong is something only you can place a value upon.
If you suspect something isn't right and a return window is about to close then you have to decide to either return it, or live with whatever uncertainty you might have for as long as you own that Mac. Or, decide to dispose of the uncertainty and not devote any more thought to it.
I can't make any of those decisions for you, but it might interest you to know it's one reason I only purchase Macs directly from Apple: I don't want the uncertainty. Resellers don't get much of a discount, and whatever margin remains has to incorporate all the overhead in selling products they purchase from Apple. In the end their sell price is very close to Apple's direct to consumer price — and in the case of Certified Refurbished products (which in many cases are current production Macs) it's often more.
Perhaps there are reasons for purchasing Macs from resellers (Sales incentives? Better return policies?) but I don't know what they are, so I fail to understand why anyone would willfully do that. With the exception of Certified Refurbished, every Mac that I have ever purchased was built literally a few days before it arrived on my desk.
Resellers... who knows what they do. I do know that there are a disproportionate number of complaints on this site regarding new Macs obtained from resellers than directly from Apple.
