Change of Title Before Completion - How Long?

Hi, I am in the process of buying a house, it is leasehold.  It has come to light that the current leaseholders (Morgeod Estates) are not on the current Register documentation.  Apparently a number of properties where not transferred over in 2022.  A request has been made to the Land Registry on 5th March - W518NTT - no update as yet.  We are in a position now where our buyer is threatening to pull out of the sale if we don't complete by 28th March (Stamp Duty). 
Can you provide an update and timescale.  
Also, legally I am able to complete on the purchase with the out of date information given that an application has been submitted? 

Hi Helen - the application was submitted on the 5th March and expedited on the 6th. It was processed on the 12th March and wider checks are now underway with the registered owner to confirm the application can proceed/complete as applied for. They have until 17th June to respond. If they respond sooner then it can be completed sooner of course.
As for the legality of completing before matters are completed then that's a Q for your conveyancer/lender and not us I'm afraid
LA190787

Thanks Adam, 
I will ask our sellers conveyancer to try and chase this with the current registered owner.  

Thanks