I believe we have discovered the key to unlimited biological disease free coral production in captive reef tanks. old tank syndrome is slain, and we can make a set of basic actions on paper anyone can copy with a captive reef and get the same results regarding longevity.
The hardware luck issues always get us at one time or another though.
Its possible to make a reef that has no biological lifespan limitation, and corals aren't just going to die of a random disease one day they just live until a hardware crash occurs or true senescence sets in roughly 400 years from now heh
its my slanted opinion that nano and pico reefs hold some of the best untapped testing for this area of science because they are so fast, metabolically speaking when you lock their sum actions inside a small container.
what a 100 gallon reef takes to manifest in aging dynamics in 15 years happens in about 2 years in a pico reef, scaled amazingly accurate in fact. try different approaches to reef designs in small reefs, see how they model out.
Once you find out how to make a small reef live 15 years, you're working with biology that when upscaled back to large reefing means agelessness.
I also think that coral loss is part of the active dynamic tank. you can't keep positive biomass at all times, seasonal changes, bad luck events and some element of hardware play will always present challenges that may result in half a brain coral setback.
but its the regrowth of the good half back over that counts and proves not due to aging etc.
there's legit coral loss, and then there's coral loss one could have engineered out much better by design.
a reef that is insulted yet grows back is strong in nature, some loss and regrowth I think is part of making these tanks strong but its not total loss where zero tissue exists to regrow.