It will be fine-don`t worry. But it is true that over time the same soil may get diseases or a deficiency of some sort.
I change mine in the big greenhouse and polytunnel over three years,using muck and stuff from the compost bins-but it is hard work.
I also use a kind of `ring culture`-10inch plastic flower buckets with the bottom cut out-the buckets are filled with JINo3 and plunged into the soil.
Stephan