Ground Rent abolishment - which date is key?

Property Investment

Hello

Hoping somebody can help.
I've had an offer on a New Build Flat accepted. The flats were completed in 2023 but were in construction since 2021. 
I am at the mortgage application stage and the mortgage lender is asking why Ground Rent is being charged, when Ground Rent was abolished on new leases from 30th June 2022.
But what date is relevent here? Is it the date that I actually purchase the flat that is taken into account or is it the date the Developer registered the lease?
I have gone back to the agency and they claim it is the date the lease was registered which is the key date. It's actually very difficult to find this rather important information anywhere online.
Many thanks for any advice in advance.
Matt