<p>Duplicate txids were made invalid with <a href="https://github.com/bitcoin/bips/blob/master/bip-0030.mediawiki" rel="nofollow noreferrer">BIP30</a> in 2012. The code was updated here: <a href="https://github.com/bitcoin/bitcoin/commit/ab91bf39b7c11e9c86bb2043c24f0f377f1cf514" rel="nofollow noreferrer">https://github.com/bitcoin/bitcoin/commit/ab91bf39b7c11e9c86bb2043c24f0f377f1cf514</a> 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).</p>

<p>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.</p>

CC BY-SA 4.0
2018-11-03T20:56:35.800Z
Theoretically speaking, prior to BIP30 could two blocks have the same coinbase TXid as an empty block within the same median timestamp and solve with the exact same nonce/PoW hash? (Assuming no difficulty change)
Mason Ticehurst
CC BY-SA 4.0
2018-11-03T21:08:29.170Z
The chances are zero, but see https://bitcoin.stackexchange.com/a/38385/60443.
JBaczuk
CC BY-SA 4.0
2020-07-01T13:09:23.420Z
If someone wants to spend transaction `d5d27987d2a3dfc724e359870c6644b40e497bdc0589a033220fe15429d88599`, how much bitcoin can they spend? 100 or 50?
Arsen Zahray
CC BY-SA 4.0
2018-11-03T05:14:16.507Z
2018-11-03T05:39:24.277Z
2018-11-03T05:39:24.277Z
JBaczuk
<p>this sounds like an old topic but i have not found a satisfying answer yet; in history there lived two blocks with identical coinbase transactions:</p>

<ul>
<li><p><a href="https://www.blockchain.com/btc/block-index/106662" rel="nofollow noreferrer">https://www.blockchain.com/btc/block-index/106662</a>
<a href="https://www.blockchain.com/btc/block-index/106692" rel="nofollow noreferrer">https://www.blockchain.com/btc/block-index/106692</a></p></li>
<li><p><a href="https://www.blockchain.com/btc/block-index/106572" rel="nofollow noreferrer">https://www.blockchain.com/btc/block-index/106572</a>
<a href="https://www.blockchain.com/btc/block-index/106730" rel="nofollow noreferrer">https://www.blockchain.com/btc/block-index/106730</a></p></li>
</ul>

<p>but if you check the receiver address (<a href="https://www.blockchain.com/btc/address/16va6NxJrMGe5d2LP6wUzuVnzBBoKQZKom" rel="nofollow noreferrer">1</a>, <a href="https://www.blockchain.com/btc/address/1GktTvnY8KGfAS72DhzGYJRyaQNvYrK9Fg" rel="nofollow noreferrer">2</a>)you would find they both get rewarded only once not twice; even though the same transaction was being used repeatedly, the two blocks have different nonces, which proved two shares of work in mining; then, which rule regards this as invalid and why is it designed like that?</p>

CC BY-SA 4.0
2018-11-03T06:02:13.607Z
Related: https://bitcoin.stackexchange.com/q/5903/5406, https://bitcoin.stackexchange.com/q/11999/5406, https://bitcoin.stackexchange.com/q/26910/5406, https://bitcoin.stackexchange.com/q/30764/5406, https://bitcoin.stackexchange.com/q/57435/5406
Murch
<block><coinbase-transaction>
identical coinbase transactions
Cyker
# identical coinbase transactions

(Asked by: username_0 on 2018-11-03)

this sounds like an old topic but i have not found a satisfying answer yet; in history there lived two blocks with identical coinbase transactions:

* <https://www.blockchain.com/btc/block-index/106662>
  <https://www.blockchain.com/btc/block-index/106692>
* <https://www.blockchain.com/btc/block-index/106572>
  <https://www.blockchain.com/btc/block-index/106730>

but if you check the receiver address ([1](https://www.blockchain.com/btc/address/16va6NxJrMGe5d2LP6wUzuVnzBBoKQZKom), [2](https://www.blockchain.com/btc/address/1GktTvnY8KGfAS72DhzGYJRyaQNvYrK9Fg))you would find they both get rewarded only once not twice; even though the same transaction was being used repeatedly, the two blocks have different nonces, which proved two shares of work in mining; then, which rule regards this as invalid and why is it designed like that?

**Tags:** block, coinbase-transaction

> **Comments:**
> **username_1**: Related: https://bitcoin.stackexchange.com/q/5903/5406, https://bitcoin.stackexchange.com/q/11999/5406, https://bitcoin.stackexchange.com/q/26910/5406, https://bitcoin.stackexchange.com/q/30764/5406, https://bitcoin.stackexchange.com/q/57435/5406  

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## 1 answers

### Answer by username_2 on 2018-11-03. Score: 4 | Accepted answer

Duplicate txids were made invalid with [BIP30](https://github.com/bitcoin/bips/blob/master/bip-0030.mediawiki) 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.

> **Comments:**
> **username_3**: Theoretically speaking, prior to BIP30 could two blocks have the same coinbase TXid as an empty block within the same median timestamp and solve with the exact same nonce/PoW hash? (Assuming no difficulty change)  
> **username_2**: The chances are zero, but see https://bitcoin.stackexchange.com/a/38385/60443.  
> **username_4**: If someone wants to spend transaction `d5d27987d2a3dfc724e359870c6644b40e497bdc0589a033220fe15429d88599`, how much bitcoin can they spend? 100 or 50?  

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