decent soil? My spare corms were thrown into a trench bordering the black currant bushes - never fed - never watered except by nature - generally ignored and I have a mass of flower....and I am on heavy clay soil. I think they thrive on neglect - but agree that overcrowding of corms could be a problem.
If you are going to reuse what you've got, separate out the corms before replanting. If buying new corms do check what height they will grow to - my rampant Lucifer are nearly 5 foot tall and have spread rapidly, but there are many other lower growing varieties in all shades from yellow through to red.