Obtaining a copy of a lease

I am in the process of selling my Mum's flat, which she left to me in her will. The estate agent has asked for a copy of the lease. I was unable to find a copy of this in the property. I'm aware my Mum extended the lease in around 2021/22. Unfortunately, the solicitor that did this work is no longer in business.

I obtained a copy of the title plan and deed online. However, these both date back to 1989, which suggests the updated documentation is not yet online with the Land Registry.

I am aware of the OC2 form, but have two concerns about this. First, I am concerned that I have very little of the information the form requires and am worried it would be returned. Second, I do not want to go through this process if it just going to return a copy of the previous (pre-extended) lease. 

Is there any other way for me to obtain a copy of the renewed lease? Or any other action I should be taking?

Tom - you should lift the relevant info needed for form OC2 from the register itself.
The register should refer to both the deed that extended the lease (short particulars of the lease) and the original lease as well (Note after the above)
Complete form OC2 as appropriate and apply by post - Get information about property and land: Get a copy of the deeds - GOV.UK 
If you are struggling with the form and register then what's the title number please?

Thanks, Adam. I have found the property on the register, but I can't see anything about the extended lease. It's entirely possible I've missed this, but I'd appreciate your help if possible. The title number is WM462137. The OC2 asks whether I'm requesting documents referred to in the register (section 7) or not referred to in the register (section 8). I'm not sure which to use here? As I say, the extension was completed back in (I think) 2022, but I can't see it in the title register.

Tom - the register hasn't been updated re any extension to the lease so it appears that no application was made to register same at the time 
There's an indication that DALLOW & DALLOW in Wolverhampton (Reference HVH/JEC/REN001/001/RENNIE) were involved in the property in 2022 and may have bene planning to make such an application but none was forthcoming - it may be worth contacting them to see what happened? 

Extension of leases (PG28) - GOV.UK
 

Thanks for your further help. That is certainly the firm that completed the extension. Unfortunately, the firm is no longer in business. Can you suggest any other way I could obtain a copy of the revised lease?

Tom - look into what happened to the firm and which other firm took over their files/records. 
SRA | What to do if a firm has closed | Solicitors Regulation Authority