You've moved goalposts. Your original claim was:

A) >It’s impossible to count how many of those abandoned transactions were successfully replayed on the new chain

now it's

B) >nodes don't know if re-org's are happening elsewhere in the network

Claim A is false as it is indeed entirely possible:

I have a chain of height 100. It is fully synced. I am sent a series of blocks diverging at height 80. I have all the information I need to ascertain which of the transactions in the two competing chains are being replayed or have been doublespent.

Claim B is true