identical coinbase transactions
Duplicate txids were made invalid with BIP30 in 2012. The code was updated here: https://github.com/bitcoin/bitcoin/commit/ab91bf39b7c11e9c86bb2043c24f0f377f1cf514 to apply the new rule "to all blocks except the two historic blocks at heights 91842 and 91880 on the main chain that had to be grandfathered in." (These are the blocks you linked above).

The reason why they received the reward only once is because a given txid can only be spent once (no double spending is allowed). If one of the utxo is spent, then both get marked as spent since they have the same txid and vout index, so only one is listed as received. It also depends on the block explorer and how it handles the duplicate txids.