[Artaud]

For me the upgrade process goes rather quickly. I just add a "B" or "2" to the existing design name, if I have only upgraded engines. If I make more than one component upgrade then I choose an entirely different class name.

I retrofit some ships right away, but often some members of the upgraded class are on patrol someplace and not near a space yard.

I regard retrofitting as an option, not a requirement. My fleets often contain modern and obsolete ships.

Sometimes I will create a specialist class for old ships. Those obsolete frigates can still give you good service if you strip out the weapons and install point defense cannons, or drone bays, or satellite bays, or supply bins, or medical bays.