Seat reservations on NEX

It seems that seat reservations on the NEX are required (we're going from Narita to Shinjuku) and that, unlike most of the rest of the JR system they can be made in advance from abroad. Problem is one never knows exactly when a flight will arrive, how long it will take to clear customs, etc. so how can you figure out which train to reserve? Or is there normally sufficient capacity that you can just show up, buy a reserved seat on the next train and board?

I do this regularly, and always just go to the counter in the Narita airport - have never not got on the next train.

However, even if it were full, the trains run quite frequently, and trust me, after a long plane flight you won't mind sitting on solid ground for 15 minutes until the next train.

Getting through Customs and Immigrations - cannot be controlled - can vary widely. Not worth booking train from overseas in my opinion.

Where is the JR or N'EX counter at Narita located? Do they accept US credit cards (i.e. Amex, Visa, MC)?

I have always made the NEX reservations upon arrival and I have always had a place. I wouldn't worry too much about it.

To get to the JR counter, just follow the signs for the JR trains in either terminal and you cannot miss it. I believe they do now accept foreign credit cards although I usually have a JR rail pass so I have not used it myself

JR-East and another company Keisei have stations of the same name in each of the two terminal buildings of the airport.
Terminal 1: Narita Airport Sta.
Terminal 2: Airport Terminal 2 Sta.
Check which terminal your flight is going to use.

As to N'EX of JR-East:
All seats of N'EX are non-smoking seats and do require reservation.
: Where is the JR or N'EX counter at Narita located?
N'EX tickets are available at JR East Travel Service Centers in the airport. This page has small maps showing the locations.
http://www.jreast.co.jp/e/travel_info/service_center/in...
If the Center in your station is already closed, find a JR Ticket Office (called "Midori-no-madoguchi") near the Center.
The two JR Ticket Offices in the airport are open from 06:30 through 21:45 by JST #.
http://www.jreast.co.jp/e/ticket/purchase.html
A N'EX train may have two parts into which it is divided at Tokyo Sta. for different directions. Make sure of your car number when you get on board.

# JST = Japan Standard Time: UTC + 9 hours

As to credit cards at JR counters:
: Do they accept US credit cards (i.e. Amex, Visa, MC)?
Of course that depends on the brand, but I suppose the three major brands you've mentioned are accepted at main ticket counters in major stations of JR-East and of JR-West, probably in major stations of 4 other JR passenger railroad companies.
JR-East says in English it accepts most major credit cards at the Centers and you can use credit cards at JR Ticket Offices.
Reservation services by JR-East (on the web in English) and by JR-West (on the phone mainly in Japanese) list at least Amex, Visa, MasterCard and Diners Club as credit card brands which can be accepted.

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As to JR reservation services:

: It seems that, unlike most of the rest of the JR system they can be made in advance from abroad

That's not 100% true, I think. As far as I know, reservation services only for some specific train services (such as N'EX) are not offered by JR-East. And, at least as to JR-East and JR-West, they are not totally closing doors against overseas on train reservation. But, regrettably, reservation services offered by them which might be available from overseas sound not perfectly convenient even to Japanese travelers (I'm a Japanese), especially to non-Japanese travelers.

JR-East is offering a reservation service on the web in English, which requires a credit card and covers reservation mainly for Ltd. Express trains of JR-East (including N'EX trains and JR-East Shinkansen trains).
Because the tickets should be collected by the night before the date of the ride, you can not utilize this JR-East service for rides on the first day of your travel in Japan.

JR-West is offering a reservation service on the phone. Though this service is usually for Japanese Language speakers, if reservation and purchase with a credit card are made at once, it covers reservation for trains even of other JR companies and allows an option of ticket delivery (to inside Japan) for early reservation. You can collect the tickets before the ride on the same day at a designated location in western Japan or, if your hotel OKs, have them delivered to your hotel inside Japan at the option.

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