Why does the original transaction timestamp and Fidel timestamps not match?

First of all, let’s quickly establish what the Fidel timestamps mean:

Now, let’s return  to the question at hand:

1.  Discrepancies between the original transaction timestamp and the Fidel timestamps may arise depending on which entity has processed the transaction and where the data has come from.

2.  The acquirer, the brand's Point of Sale (PoS), the Card Network, the Issuing Bank, the Payment Processor will all potentially have slight deviations of the transaction time right down to the second. 

3.  We aren’t able to do a lot about the above factors, as they are generated by external entities. However, there are other alternative, unique transaction identifiers that can be used to match transactions depending on which entity is being represented. 

• • The Authorization code (within the Fidel transaction object) can be matched back to a brand's PoS. 
  • An Issuer reference number (Not within Fidel transaction object - for data privacy reasons) can be matched back to an Issuer transaction.