Once you locate and identify one of the rhizomes that's growing out from the crown, loosen the soil below it and follow it back to the crown. You should be able to see if there's any life left in the crown and replant the new ones if necessary. If you originally started with rhizomes, what you're digging up is the exact same thing, plus or minus some new growth and should be treated like any other first year rhizomes.
One growing season after you plant a rhizome, you can technically call it a crown because it's developed a root system of it's own and has formed buds that will grow into new shoots the following spring. A year or two more, and you can call it a mature crown meaning that it has most likely accumulated enough excess energy to start producing rhizomes of it's own. Once these form, they can grow out away from the crown for quite a way each year (3 feet is not unreasonable, especially in sandy, loose soil). If you have two plants spaced 5 feet apart, you may have rhizomes from each grow together by the end of the year. If you have room, you can plant them farther apart to help keep this from happening. If you don't, you should plan on starting to do some root pruning (rhizome pruning more accurately) at the beginning of the 3rd year. Just dig a trench around the crown and cut back any rhizomes you find. You won't set the plant back and will help keep it from spreading. Hope this helps.