To be clear, you're describing something not possible in our universe or any set of universes I can conceive of. Right?
There's no way to gather selves across worlds or somehow sense what's happening to other versions of you.
Say, moment-to-moment, your observation-moments were cycling as follows:
A -> B -> C -> D -> E -> A
A, B, C, D, E can be like features of your epistemic position
there can be other things as well, but there's that cycle for sure
as you move through the world, that cycle keeps occurring, but maybe other features of observation-moments for yourself vary.
Say, through actions, you went near the fuzzy Anthropic Shadow boundary and then away from it, and then your cycle was like
A->B->C->A
You've lost D and E
So long as you remembered the ABCDEA cycle, you know you lost parts of it
this isn't necessarily how all the cases look - it's more illustrative
Like - you don't have to have the selves be counterfactuals of you that are inaccessible - it could be like flickering versions of you moment to moment
This is possible if what "you" are is relaxed so that you've got multiplicity. If you, as an observer, transform and cycle through different kinds of observers, you're an ensemble of shapeshifting you's. If you could relax your sense of self, ambiguating who you were, and perhaps expecting all your selves to recombine at a later point - you could notice when you were not able to fully collect all of your selves. If you're forced to disambiguate, that could indicate your measure was lost.
This sounds as if you are describing an action that a person can take, and an observation you can make of the results of that action, but I can't make out what the action or the observation are.
Translating the "Anthropic Shadow" into mundane language, are you saying, "when you notice you have had a brush with death, learn from the experience to better stay away from it in future"?
The action might be something like: varying your behavior in such a way where you're shifting the nature of yourself as an observer often and along several axes.
If you track the ways you're changing and notice when some of them disappear, that'd be the observation.
Regarding the "brush with death" bit: yes, that seems like some way to put it. Of course, it's more interesting the more you can detect directions towards/away from doom that may be unintuitive, and if there's a skill here you can refine.
There is an observation that 10 000 rule's violation results in 100 near-miss accidents and 1 death (not exact number, just my approximate memory and can vary in different situations). A person can calculate the number of near-misses he survived and calculate if he is affected by survivorship bias.
The Anthropic Shadow is the wall of worlds where observation stops — you can't observe events incompatible with your survival.
I wondered if the Anthropic Shadow could have fuzzy boundaries. What that would mean is that the Shadow would prune some of you as you approached it, but not all of you. Furthermore, it would prune more of you the closer you got to it. If the Shadow weren't fuzzy, then the only way you'd know it's there is the logical implication of your demise placing you into observable worlds. The fuzziness lets you know when you're close.
This is possible if what "you" are is relaxed so that you've got multiplicity. If you, as an observer, transform and cycle through different kinds of observers, you're an ensemble of shapeshifting you's. If you could relax your sense of self, ambiguating who you were, and perhaps expecting all your selves to recombine at a later point - you could notice when you were not able to fully collect all of your selves. If you're forced to disambiguate, that could indicate your measure was lost.
I'd say that you've sacrificed your selves to the Anthropic Shadow Realm. In doing so, however, many of your selves continue to persist and you've got some information about where the wall is, so you can steer away from it. You might be able to tell when some of your selves went missing if you found a way to keep track of various properties of yourself.
The idea reminded me a bit of virtual particles splitting at the event horizon of black holes, since some can disappear into them forever, while others are released into space.