Joe,

Factors to consider include:
1. Cross section coupon to verify the line width and copper thickness.
Reduced line width has a significant direct impact on raising the impedance.
2. The same above cross section should also show the dielectric distance
between the signal line and the ground reference plane.  Greater dielectic
thickness will increase the impedance value.
3. Run some "old" coupons on the TDR and see if the values can be repeated.

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