[A] Yes we can add backdated stock in the TranZact Inventory.
[B] In order to add the backdated stock, we will have to use the physical stock reconciliation (PSR) option.
[C] While doing PSR the field "As On Date" can be used to add the backdated stock.
[D] Choose the date for which you want to update the stock and follow the normal steps of PSR, your stock will get updated for the date you have chosen.
Here the article to know how to do physical stock reconciliation -