It is always subtle, never predictable, and progressive but it never progresses at the same rate. But one of the big sign is when you open one file and get a different file (in this case, if I’m right, OH is loading nodex.xml and getting nodey.xml) or you delete a file and it comes back, log files fail to rotate, changes made to files become unmade after awhile, etc.
But the failures are highly localized. The whole card doesn’t wear out all at once. One sector at a time wears out as it reaches its max number of writes and stops responding. Since most of the writing that takes place on these systems are not done in ways you would necessarily notice unless you look for it (e.g. logging) it is possible for a card to be failing for quite some time with no outward symptoms. I had a card fail and never knew it until my log file filled the card because the log rotates were failing. Everything else worked just fine, though the longer I ran more and more problems would occur as more of the card wears out.
I’ve seen people say it is possible. I’ve never don’t it myself.
Search the forum for “symlink” and a bunch of posts will be in the results.