It's actually the other way around. The Land Office has the original and the person named on the title deed holds the copy.
If the deed is old then it is possible it has been renumbered/resequenced. When this happens the title deed can sometimes get slightly misfiled in the new sequence, which means a more thorough search will be needed to find it. This has happened to me once before and it took an hour or so for the Land Office to find the missing deed.
That being said, all NS4 chanotes have been digitised, and all the relevant particulars are held on the Land Office computer systems.
However, if the buyer wants to sell the land they must appear with their title deed on the day of the sale, unless the property is mortgaged, when a representative of the bank will appear with the title deed.
No deed, no sale. That is absolutely final. If the deed has been lost by the seller, then the seller will have to go through the process of obtaining a duplicate title deed from the Land Office. This can take some time.