To be honest, no one seems to really care what the date on an IDP is, certainly not in Japan. If it does have a date, when it expires, just put a sticker over it and either stamp or write in a new date -- hey presto, you have an IDP good for another year for free!

This whole IDP thing is surely regarded as a profit center by the AAA.

That doesn't strike me as a sensible way to save £5. YMMV.

I have ones effective 2015, 2016 and 2017 (each one hand-written). Might be able to change 6->8, 7->9 lol.

Thought I'd add a quick heads up for something I only learnt very recently. Just like JR passes it's possible to buy an ETC pass for different regions. This is only open to foreign visitors and gives you the chance to pay a flat daily rate which covers all tolls. Given the cost of tolls in Japan it can easily save hundreds of dollars in just a few days. Here's an example for Kyushu

KEP Kyushu Expressway Pass - West Nippon Expressway Company Limited.

Some more information on tolls and passes here:
https://www.japan-guide.com/e/e2354.html

AAA in the USA is charging $20, but anyway, that's not the main reason -- it's saving the hassle of having to get it. And ir really is irrelevant. No one keeps a database of these international driving permits, their sole purpose is to give information in multiple languages, so who cares about expiration dates? No one, except that at $20 they are a wonderful profit center for AAA.

Thanks a ton for this very useful information.

Fiance and I are going to be honeymooning in Japan for 2 weeks at end of July/beginiing of August.

We are staying in Osaka and Tokyo for about 1 week each. We are thinking of doing a mid-stop to hike Fuji, and were planning to rent a 1-way car from Osaka to Tokyo with a stop at Mt Fuji so we can hike to the top - question is....is there parking at those Fuji base stations? We're looking to do rental car since are are trying to get a very early start to try to do a sunrise...and it will be more convenient if we can drive ourselves from Osaka to Fuji.

Thanks for any help!!

If it were me, I'd rent the car somewhere near Mt.Fuji along/near the bullet train route from Osaka to Tokyo. Like Mishima or Gotenba. That way, you can avoid city driving (esp if you're renting from Gotenba). The bullet train kodama stops at Mishima. Regardless of where you rent, make sure you rent from a place that's right near the JR train station so that you get off the train and it's an easy walk to it. Driving in Osaka and Tokyo would be really difficult and intimidating for me personally, even though I read Japanese. On the other hand, I think it would be nice to have a car to tour around the Fuji area. I don't remember the parking situation at Mt.Fuji too well, except I know that there is a fair amount of parking available at the 5th station.

Be aware that there are restrictions on private vehicle traffic on the routes to the 5th stations, with the exception of the Gotemba route.
Access / Vehicle Restrictions | Read before climbing | Official Web Site for Mt. Fuji Climbing

Dang, ok that is VERY useful to know. Thanks a ton for the word of caution!

Has anyone rented a car using a third party booking site like Tabirai or Jalan/Rakuten (JP versions)?

Tabirai's price for an Orix rental beats booking direct for a similar car for some sample dates. English Tabirai indicates CDW is included, but prices are higher and state they include an English navi. JP Tabirai has something along 免責補償込み which translates an indemnity compensation and which Orix offers as an add-on CDW.

An ETC reader would be helpful if I wanted a freeway pass or ETC rental card, but as far as I can tell, a 2-day pass in Kyushu starts at 3,500 yen while I just need the segment between Oita/Beppu which is < 3,000 yen. Could I just pay the tolls using US credit card or cash?

I think every single rental that I've done in the last few years has been through Rakuten (Jpn version). Although I haven't checked every single time, it just seems like Rakuten offers same or better rates and availability than booking direct. Plus I don't have to deal with having to go to different websites and signing up for different username/password, etc. When I book cars through Rakuten, I don't pay Rakuten but rather pay the rental agency directly at the counter and I'm bound by that agency's rules as far as rental terms, insurance waivers, deductibles, etc (although that will also depend on the type of plan you choose). Rakuten is merely a platform for securing the reservation in that regard, as opposed to booking a car in the US through a third-party site. Yet you still collect Rakuten points. So as of now, I see no downside to using Rakuten for rental car bookings.

You can pay expressway toll via credit card... at least you're supposed to be able to. But, for some reason, my Chase VISA was declined ONLY at Jpnese expressway toll booth the last two trips that I rented a car (the same card worked everywhere else in Jpn). Each time I had to then present another card (AMEx) and that worked. Expect to be able to pay by card. But I agree that it's a good idea to have some cash on hand just in case.

Most people on FT would not be comfortable booking cars in Japanese and may find it more feasible to go through an English website such as Tocoo. But since I'm Japanese, I've never used those websites before.

I think it'd be helpful if someone who's familiar could post some details about the easiest way for a non-Japanese person to book a rental in Jpn, how Tocoo (or another equivalent website) works as far as the rental terms and who processes the payment, its pros & cons, etc.

I used Tocoo last time I was in Nagano. The staff at the rental office doesn't speak English and called Tocoo customer service and have a guy do live translation for me. If I recall correctly, all I did was book & pay through Tocoo, print out the confirmation email, show up at the rental office with my passport, Canadian driver license, international driver permit, and the credit card I used to make the booking and that's it. I don't recall getting dinged for service charges but some people online did say they do sneak in stuff like that. Read the fine print.