a hidden markup in a dealer's favour? Who was the client? What tier of pricing are they on?
What's the counter currency? If it's CAD or TRY then spot is T+1 not T+2.
But I think "nonefaster" has the answer.
What does the NZD roll forward time mean? Do you mean, say, that the forward desk changes its pricing source from London to New York? The forward trade date and value date are calculated in which timezone? And what relation does this bear to the spot desk?
Tell me the exact trade date (when the client order was executed) and what value date was asked for? If the client specified a value date rather than a tenor then what "nonefaster" is saying kind of makes sense. But not 100% because your client either asked for a specific value date of Tuesday, or a SPOT tenor (T+2) and the counter currency is neither CAD nor TRY...
If your client asked for a specific value date of Tuesday, or a SPOT tenor then how did your back office made the deal value date the following Monday... T+1 and a TOM tenor? And what is your back office doing adjusting prices?
There were no holidays involved in NZD, or in the counter currency. If the client asked for SPOT and the forward date rolled (which it couldn't for a SPOT tenor because no forward adjustment takes place) then the value date would be Wednesday :)
But it looks like the deal was thought to be a TOM by the front and back offices, and price was adjusted by the pre-spot forward pips and that's the difference you've seen.
If there was some kind of "hidden markup" it refers to a spot spread adjustment in the NZD (or the counter currency) that was applied to the forward deal, or a forward spread adjustment applied to the forward component. But that ought to depend on the client credit tier (as in first question above).