cashing in unused juhachi kippu

I know that if you buy but dont use the juhachi kippu at all you can return to JR offices for a refund - ( for ex if your travelling friend got sick)
but I have heard that you can also cash in any unused days at a ticket sales office (Pia?) is this so ?
Any info would be great as i think I cant use all the days on this seasons ticket I have bought.

All you can do is to take it to a discount ticket shop and see if they buy it. Of course
they will buy it for a price far under the original price, so that they can mark it up and still sell it to another customer for an attractive price. NOte that the closer you get to the end of season, the lower their buying price would be.

I don't know where you are, so I cannot give you any name for the "discount ticket shop," but maybe you can ask at your hotel if they know a "kinken shoppu." (When someone told you "ticket sales office," they were not talking about places like Pia, but those discount shops for unused train tickets and other types of tickets/coupons.

If it is possible to cash in the unused part of your 18 kippu, it will be at a discount ticket/coupon reseller (kinken shoppu) rather than an event ticket sales agent like Ticket Pia. Kinken shoppu are usually found somewhere near a station and have discount movie tickets, vouchers etc. in glass cases. They can be a bit difficult to find if you don't have someone to show you where one is.