Longevity of Swages???
I don't think anyone really knows how long a swage will last! My dad changed his standing rigging for the first time this winter on his 1972 Bristol 40. He is the original owner. I certainly don't advocate going 38 yrs! Maybe it was better metal! Boat was never raced, he was never one for very tight rigging, and he left the mast up most years. The boat was always covered in the winter so minimized exposure to the lower swages. On changing it, no broken wires or obvious cracks were present. (god knows what it would have looked like under a microscope)
In contrast, the boat I race on Weds nights, had rigging failures on 3-4 yr old swaged shrouds. On inspecting the lowers before raising the stick, I noted broken strands. The shrouds were made up by a local reputable rigger. The other side had same problem last yr.
I think with a trailer sailor it is very important to spend a lot of time avoiding bends in the rigging.