Papua New Guinea 10 Kina - Both These Coins Proof?

My Krause catalog gives these grading definitions:

FM - Franklin Mint, U.S.A.
NOTE: From 1975-1985 the Franklin Mint produced coinage in up to 3 different qualities. Qualities of issue are designated in ( ) after each date and are defined as follows:

(M) MATTE - Normal circulation strike or a dull finish produced by sandblasting special uncirculated (polish finish) or proof quality dies.
(U) SPECIAL UNCIRCULATED - Polished or prooflike in appearance without any frosted features.
(P) PROOF - The highest quality obtainable having mirrorlike fields and frosted features.

Here is where I am confused. When consultation NGC for Papua New Guinea 10 Kina KM# 8a, I only see the coin with the dark mirror like finish and a listing of 1975FM (P) Proof. When I search Papua New Guinea 10 Kina KM# 8 instead, now I see both both 1975FM (M) and 1975FM (U).

How do I learn to tell the difference? I have 2 silver coins with a different look/finish. Are they both proof? Both weigh the same.

Krause and NGC both do not provide the gram weight of a copper-nickel 10 Kina, and the coin size is the same. Supposing one is a copper-nickel, I have no apparent way to determine that by weight, if both C-N and Silver weigh the same.

As an interesting side note, I once bought a certain Panama Balboa coin with erroneous silver content. I believe it was KM# 39.2 BALBOA. It was stamped indicating silver content but had none. Both C-N and Silver coin weighed the same. If I recall right, the only way to differentiate between the 2 was a fine reed for the true silver coin.

So, were C-N New Guinea coins erroneously stamped silver? Is the edge reed the only way to differentiate? I'd like to learn more about this.