I'm confused about reservations

Found the following on the JR East site under Q&A.
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"What is the time period during which reservations can be made?

Reservation procedures all use Japan Standard Time (GMT+9). Reservation requests are accepted during the period from 10:00 a.m. of the day one month before the departure date to 17:00 (5:00 p.m.) 3 days before the departure date.

You must collect your tickets by 9:00 p.m. (21:00, Japan Standard Time) the day before the departure date at the designated location within the JR-EAST service area. If you do not collect the tickets by then, the standard fee will be charged, and the reservation will be cancelled.

There is no fee for refunds or cancellations made up until midnight (24:00, Japan Standard Time) 2 days prior to the departure date, but the standard fee applies after that."
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Can someone please shed some light on this info. It seems to me to indicate we can't arrive in Tokyo, convert our JR pass and then reserve a seat for that day?

... using the online reservation site. That is correct,

But you can still make reservations at the ticket counter on the day. Are you planning to travel on a busy day on a busy route? Note that most trains do not get booked out (far in advance) except on busy days.

Great now I'm clear on that....
Ideally would like to travel on the Sunrise Seto the evening we arrive in Tokyo(25th Dec).
Given this is well patronised even on regular days,is there anyway to reserve seats before we arrive in Japan and activate our JR pass?
I'm not confident of our chances of securing sleeper cabins for 6 on the same day. I would appreciate your thoughts.

Yes, I am afraid, chances are high that the specific train will be already booked out. I can't think of a way to make reservations from outside Japan, except if you have somebody in Japan who can make reservations for you.

Ok,.. so if I can arrange for someone in Japan to book us on that particular train ....
1) Would we still be able to use it as part of our JR pass with the usual sleeper surcharge?
2)Is it then possible to collect the tickets from the JR Narita office when we arrive?
Appreciate your help so much!