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Logic Puzzle #39: Coincidental Overlap or Not?

Spectral data is just data until you can see the bigger picture. This puzzle looks at a scenario of quaternary carbons.

For an unknown compound, a standard 13C NMR spectrum (500 MHz CDCl3) was collected. The expanded region below shows 4 signals. Is the signal at 172 ppm attributed to 1 or 2 carbons (from an amide group(s)) if the remaining signals represent 1 carbon atom each? How can we test this?