Do you mean this list? https://www.learningtheharp.com/songs-in-order-of-difficulty/
If you take a look at the more difficult songs further down the list, there are actually several pieces that you only need 26 strings for. There is no “limit”, there are only a few songs that you’d have to adapt for a smaller harp. I actually learned both the intermediate version of “Hallelujah” and “Perfect” on my smaller harp before I upgraded to a 34 string harp, Christy-Lyn includes instructions on what to change on smaller harps in both these courses, although they’re listed as needing 33 or 34 strings. Intermediate Danny Boy, Yesterday and Can’t Help Falling in Love are significantly trickier to adapt, but even if you steer clear of those 3, you can learn all the other songs on the list except for 3. That’s pretty great!
Also, as someone mentioned above, Christy-Lyn has made a conscious effort on making each new piece accessible for smaller harps for some time now, and she’ll keep adding a new lesson each month, so I don’t think you’ll run out of options any time soon.
Courses in Order of Difficulty