I think you might have drawn the wrong inference about what the rule for numbers is. The wrinkle in this level is how to satisfy the rule for the three without compromising the application of the rule to the two, which then dictates the way the thread has to move through the SW portion of the level. The position of the three in this case means there's only one way to satisfy the rule here, as was also the case for level 16.
If you're super, super stuck, I've rot13ed what I believe the rule for the numbers is:
Gur ehyr sbe ahzoref vf gung gur guernq zhfg gbhpu gung gvyr ba gur fgngrq ahzore bs fvqrf, vtabevat qvntbanyf.