Good morning!
I assume you are referring to the measurements made by the Voyagers as they traverse through the solar system's magnetic field and into interstellar space. The model scientists had of the "heliosphere" before the Voyagers was based on observations of magnetospheres of the planets (including Earth). But we now have data that shows the heliosphere is somewhat different. This is a great example of how science works. Theorists use data to create a model or an idea of how a system works. Experiments (like the Voyagers) collect data. Then the models are corrected to take into account the new data. This often requires a deeper understanding of the physics involved. Then new experiments are performed and the cycle continues.

For more information and to see the difference between the old and new view, see this website: https://svs.gsfc.nasa.gov/10790