Hello, this is Dr. Linda. I hope I can help with your question today.
I really do not think you have anything to worry about with this puppy. In order to have any chance of a problem, you need to breed a merle ( Aussie, Great Dane, etc. ) to another merle. In other words, you need a homozygous combination of genes. The merle coat color is not present in the Labrador, so just because the coat pattern popped in this pup, there is almost a non-existent chance that any further defects will manifest in this puppy.
We do not fully understand all the particulars of this defect, but a coat pattern that results in a lethal combination will happen in other species, too, such as lethal white in horses & lethal trait A46 in black pied Danish cattle.
So, your pup has enough hybrid vigor to eliminate any chance of any of the unfortunate conditions associated with a homozygous merle coat.
I hope this makes sense & has addressed your question. Please, if you have any further concerns, or I can help in any way, do not hesitate to ask.