The YQ on OZ F ICN-JFK is $15:
<snip>
And on a RT, ICN-JFK-ICN, it's $30:
<snip>
And the YQ on OZ F JFK-ICN is $140:
<snip>
And on a RT, JFK-ICN-JFK it's $280:
<snip>
So it seems like OZ charges nominal YQ when departing ICN (OW or RT), and significant YQ ex-USA (OW or RT).
That being the case, am I to assume the reason that the highlighted charge in the below itinerary is assessed is because it's a RT ex-USA, even though the outbound is NOT on OZ metal?
<snip>
If so, the lesson here is if you're booking OZ F with miles where you incur YQ, make sure to book them as OW and NOT a RT.
First, I'd like to point out the varying fare codes Matrix is using in your screenshots: ex-ICN is
FOW (First, one-way) and
FRT (First, round-trip), while ex-NYC is
AXSUITE, except for when you have an Air China outbound, then the OZ return is
F1. I'm not gonna go into the technical ramifications of that right now, because it will get too confusing... but just something to keep in mind.
Now, as for the YQ mystery, the answer lies in the fare rules. The ones Matrix links to are a bit abridged, so here's an excerpt of the full version from Sabre (Category 12: Surcharges):
...AND - ORIGINATING KOREA REP OF/SOUTH -
FOR TICKETING ON/AFTER 01FEB15
MISCELLANEOUS/OTHER SURCHARGE OF USD 15.00 WILL
BE ADDED TO THE APPLICABLE FARE PER ANY
PASSENGER. blah blah blah... AND - ORIGINATING UNITED STATES -
MISCELLANEOUS/OTHER SURCHARGE OF USD 170.00 PER
FARE COMPONENT WILL BE ADDED TO THE APPLICABLE
FARE PER ANY PASSENGER. Aha! There's the discrepancy! But why $140, and not $170? Beats me. One possible clue lies here, a little further in the fare rules:
THE SURCHARGE MUST BE COLLECTED AT TIME OF TICKET
ISSUANCE AND WILL BE INCORPORATED IN THE FARE
CALCULATION AS A -Q- SURCHARGE BY CONVERTING
THE SURCHARGE INTO NUC USING THE APPLICABLE
IATA RATE OF EXCHANGE /IROE/. NUC stands for "Neutral Unit of Construction". It's a fictitious unit of currency, equivalent to USD, used by airlines and governments for calculating prices of airline tickets across currencies. I'm not gonna go into details now, except to say that this "imaginary currency" can screw things up (remember a couple of weeks ago how tickets were cheaper on Russian sites due to "currency discrepancies"?) So, it's entirely possible that in the process of changing between USD, NUC, and KRW (Korean Won), $30 is lost due to exchange rate discrepancies. Maybe... if anyone has a better theory, I'd like to hear it.