1. Genesis Block Reward: The original 50 BTC from the Genesis Block (the first block on the Bitcoin blockchain) cannot be spent. Most block explorers recognize this and don't count it as part of the balance. However, discrepancies might arise if some explorers mistakenly include it or handle it differently.

2.Double-Spend Transactions: There might be transactions that are double-spent, where one version of the transaction is included in one block explorer's database but not in another's. This can happen due to differences in how explorers detect and handle double-spends.

3. Orphaned Blocks: If a block was orphaned (i.e., not accepted by the network as part of the main blockchain), the transactions in it might be counted by some explorers but not by others.

4. Unconfirmed Transactions: Some explorers might include unconfirmed transactions in their balance calculations, while others only count confirmed transactions.

5. Software Differences: Different block explorers might be running different versions of their software or Bitcoin node software, which could lead to differences in how data is interpreted and displayed.

6. Manual Adjustments or Errors: There's also the possibility of manual adjustments or errors in the data used by these platforms.