I swore I read in the Mary Roslin Williams book about Labs that those that show tan points are drawing back on genes from when possibly dobermans and rotties were mixed into the breed. I think in her day of raising and breeding labs, if those colorations showed up, they were usually a bit suspect in the temperment area, afraid that they might have lost some of the labrador temperment by recalling those genes of the guard dogs...
But truth is, color is nothing but color in labs. Whether your choco has tan points, or you got a yellow with a big old black ink spot on it's back, it's just a plain old mismark.