I'm not able to give you what you what you're asking about.
But early on, I found the following article extremely helpful in evaluating my risks and deciding on treatments. It was written by one of the most brilliant ITP minds in the world and has been my personal guidepost for decisions about my treatment. The part that struck me most is in the first paragraph relating to adult management of the disease. It talks about half the observed deaths being from treatments, not from the disease.
link.springer.com/article/10.1007/s12325-015-0251-z
Catastrophic, spontaneous bleeds aren't uncommon in people over age 60, but they are uncommon at younger ages. Risk relates more to the sturdiness of blood vessels than to platelet count per se, and old vessels are flimsy and prone to bursting without warning. But that's true even in the elderly without ITP.
Very low counts feature supersized, efficient platelets that can do an exceptional job of clotting when needed.