The first thing to know is how coins are made , what process they go through and quality control.
With that in mind, understand the US Mint strives to produce even quality coins from the first to the last. This was not always the case but is the norm now. So with laser etching and powerful presses and a quality control program they now produce tons of mint 70 and proof 70 coins.
Enter the LABEL . First strike , early strike birth set etc... these coins were struck at the Westpoint mint but no mint mark... It does not mater! Why pay a premium for a coin that is unidentifiable without a label? You take a bunch of identical coins and put them in different packages and that makes them worth 20% more? Almost as obnoxious as a CAC label , paying a premium to grade the grade! Now that is a slap in the face to NGC. I can understand on a real expensive coin you might feel its worth to have a second grade of the already heavily scrutinized grading , that may be worth a CAC label . But without any other difference to a coin than a solid mint mark, why bother. With the exception of a signature.
I can buy a set of ms 69 ASE dollars for 2 thousand $ or a set of ms 70 for 20 thousand $... So what happens when my 20k set develops milk spots 5 years from now?
Bottom line buy the coin not the label!