Hotel Ambassade does not provide the Rick Steves discount mentioned in both guidebooks

This hotel is wonderful and in an perfect area of Amsterdam, on the Herengracht Canal.

Not uncommon. There’s only so much they can discount and still remain in business. It’s like trying to use a coupon that has a disclaimer that says it can’t be used on sale or discounted merchandise.

My take is that discounts are just gimmicks to try to get people to use a certain "channel" to make the booking. I ignore them and just compare prices when that hotel is listed on multiple channels. In this case, the channel is a certain guidebook (and both the hotel and the guidebook writers benefit). But there are multiple ways to book a hotel room and each can have its own distinct set of discounts or none at all - whether it's a guide book, or a third party site that gives some percentage off for using that site, or the hotel's own loyalty program or discount-of-the-month. The point is discounts are easily manipulated and changeable depending on whether the hotel needs to "move" certain rooms that would otherwise be unbooked. So what I would do is not focus on a single guidebook's recommended hotels (and discounts to drive you to that hotel) but to look very broadly and compare room prices for that hotel (and ones of similar quality) using every avenue you have available: whether its booking.com, hotel website, guidebook, other third party site, etc. You'll discover that one discount can beat another discount, or that a discount is nothing but "noise" in the grander schemes of things (since you can get a better base price elsewhere without any overt advertisement of a discount). All that matters is the total room price with taxes/fees. So I would advise to compare and not just go to exclusively with the hotel website just because a guidebook that has some relationship with that hotel tells you to do so. As a caveat, I am not a believer in booking directly with hotels if I can get a better price elsewhere, and most of the time, I do.

I know nothing of this particular hotel, but one thing to keep in mind is that the owner may not want to commit to discounts for almost a year out. I’ll assume it falls in the locally owned type place that Rick favors.

There’s a lot that could change between now and May of 2019. If something changes, the hotel may need to charge higher rates in 2019. And, in your favor, if the economy falters, the current rates may come down. Unless there’s a major event happening then, I’m not sure I’d book so far in advance. It’s fine to start planning in advance, but I’d probably wait until closer to May to actually book. February or March should be fine.

As a former hotel owner I can say with confidence discounts are not gimmicks...however...almost anyone anywhere can get a 10% discount off rack rates for almost any reason...it’s built in to the price already. Hotels often have different levels of discounts depending on who you are and who you are affiliated with.

This seems to be a problem of communication to me more than anything.

And the hotel is more than likely telling the truth. That 10% goes to Booking .Com and the other cohort of aggregators/bookers/travel agents etc in the form of commission on the rooms. This is why many people advise as I do to deal directly with the hotel. It is almost always cheaper.

So this is a case where probably everyone is correct. That is not to say that this hotel might not be playing games too. Amsterdam is not my favorite city for hotels and their practices sometimes.

As a former hotel owner I can say with confidence discounts are not
gimmicks

I didn't say they weren't honored (most of the time). I said they were just shiny objects that people pay too much attention to, and it's not worth putting too much stock in them (since there's a dime-a-dozen different discounts depending on a variety of factors). Printed guide books in general can't be counted on to have all their info up-to-date especially when it deals with restaurant and lodging pricing, including discount rates. I would write to the RS folks directly and ask them to amend their entry for this hotel so that other people don't have their expectations crushed.

And as someone else said, it is really early to look for lodging for May 2019. You have plenty of time to shop around and get a nice hotel. I would not rule out third party sites like booking.com. Guidebooks need some competition as a pipeline for hotels, and third party sites have a much larger selection to choose from (and actual reviews).

I have read other online accounts about hotels claiming they never offered a "Rick Steves Discount", even though one was mentioned in a guide book.

After I've picked out my hotels, based on my own system, I always check to see if my choices are in the guidebooks - if the town is included, my choices are in the books about half the time.

I think this information is important to report in the guidebook feedback on the website. If everyone gets a 10% discount that books directly with the hotel compared to going through a third party booking site, then that’s the accurate information I would want to see in a guidebook. For the guidebook to say there is a Rick Steves discount when there isn’t is false and should be corrected. At one time a RS discount may have been given but things change. That is why feedback should be important to Rick Steves.

If everyone gets a 10% discount that books directly with the hotel
compared to going through a third party booking site

It's worth noting that guidebooks, hotel websites, and third party sites often have different room base prices for the same room, and discounts make this less obvious for a consumer (they'll think...great! I'll go with the place that offers a discount because it will be cheaper. That may or may not be true, and the only way to know is to compare prices for the same hotel, same room across different booking channels). No guidebook or hotel will tell you to check prices on an alternative site, so it's not exactly accurate to say 10% off for booking directly with a hotel "compared to" a third party booking site. The hotel will not disclose what other sites offer because they want you to book directly with them. A 10% discount just means 10% off some rate they are offering at that point in time. But I agree that RS guidebooks should not make discount claims if they're easily refuted; at least they could put in a caveat that says this is the best info at time of print and leave it at that. If customers bring it up to their attention that such a discount seems to have not existed, then it should be removed.