1911-D $2.50 Question about mintmarks

Does the weakly struck mintmark have less of a premium over a strong mintmark?
If so, how much would the price be affected? If not, why do TPG's label "Weak D" on the label?
If so, how much would the price be affected? If not, why do TPG's label "Weak D" on the label?
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Here's the PCGS price guide for your reference:
Link