Some posters above make it sound like once the A-rated SCOs are released, you have to immediately refit your entire fleet with them. Which is pretty much not neccessary and very unwise to do.
A very similar thing already happened to FSDs once, with the introduction of the double-engineered ones. I eventually refitted all my ships that had a c5 FSD slot with the better modules, but only gradually, over the course of a couple of months IIRC.