As long as you researched the tech first, 10% instead of 100% doesn't matter. A forested grassland cow will make 3 shields per turn (a mined plains cow will also make 3 shields per turn). The AI doesn't prebuild. However, if a wonder gets finished by someone, and another AI was building that wonder, the other AI will switch to another wonder, if they have one available. E. G. Sumeria finishes the Temple of Artemis. Babylon was also trying to build the Temple of Artemis. So, Babylon switches its production to the Hanging Gardens. People usually refer to this by the term "cascade".