I know this sounds picky, but these trips are vacations for me, not so much "training opportunities." Except for my trip to Spain, I didn't really do any special training, and that was only because it was so early in the season. I tend to just push through, grin and bear it, as I know I can get through horrible climbs based on what I do at home. I may be slow, but I can do it. The only reason I didn't do some of the "extra" climbs in Spain was the fact I was on a rental bike where I could not reach the brakes from the drops and the lowest cog was a 25, as opposed to the 27/28 I have on my carbon roadie.
This is somewhat of a digression, but over the years I have learned a lot about myself on these trips. Each one had its plusses and minuses. Spain was definitely the best, due to the small, international group, and the leaders, who are the actual owners of the company. The riding was horrifically hard (we did 2 climbs that were on a Vuelta route), but the other parts, especially the food, made up for it. The trip to the Finger Lakes was the worst, mostly due to the weather, but I also found the scenery to not be that wonderful, coming from eastern Massachusetts, and we were riding on roads with wide shoulders, but filled with debris. I had 5 flats on that trip, and 2 more when I got home, when I finally bought new tires.
A lot to think about.
When dearie and I plan cycle -touring trips together for just the 2 of us and cycling with our own gear, he tries to be reasonable in his trip planning. Meaning routes that don't expose us to lots of high dangerous speed car traffic, etc. The trip is for us as a couple but each of us have slightly different interests. For certain he does not approach 500-1,000 km trip with me as a way to test our cycling limits, etc. Hill climbing is kept around 6-15% grades. We are packing in 100km. on some days, while other days it can be down to 30-40 km.

Of course, he doesn' tell me in super great detail what lies ahead on some trips. I don't need to know all the difficult points and in a way I don't want to know all the detailed tough stuff. But only enough that I am alert /can expect what to see along the way.

There are always some unknown/uncontrollable factors in a trip but one does try to choose the best cycling seasons for an area.