Hi, Colleen. Root congestion is an insidious robber of your plant's potential in terms of growth and vitality. Symptoms include limited growth or no growth at all, and on branching plants, most growth is concentrated near the tips of branches (branch apices) where extension growth takes place. This occurs by way of shedding of oldest leaves and leaves closest to the trunk. The stress caused by root congestion can first be measured in the roots before the visual cues mentioned become conspicuous. When the roots of your plant become congested to the degree the soil/root mass can be lifted from the pot intact, the plant would benefit from repotting or dividing, depending on how its roots are structured.
What changes (in your care regimen) did you make that might have caused the plant to turn around? Typically, plants 10 years old that call the same pot 'home' for that time span don't just suddenly decide to start growing like crazy.
Also, there is a significant difference between repotting and up-potting or potting up. The former eliminates all stress associated with root congestion until it eventually becomes an issue again. It includes bare-rooting, root pruning, and a change of grow medium. Potting up is easier, but doesn't eliminate the stress of congested roots; rather, it ensures that root congestion in the middle of the root mass remains as a limiting factor until a pair of hands gets into the center of the root mass to correct the congestion and remove heavy nonessential roots.
Al
