Do fly rods weaken or lose their action after extended use?

During the late 1950s and 1960s, I used Fenwick FF85 rods. There was no question that after long and hard use, the blanks would soften and the action would slow a bit. I had Temple Fork Outfitters check with legendary rod builder Gary Loomis, who replied that modern fiberglass rods will not soften or change in action simply from being cast. Nice to know.