AST Tenancy 3 years with Landlord break in 12 months

Hi all

I hope someone can help answer the new S21 6 months notice period a landlord needs to give a tenant.

I signed a new 3 year tenancy with a landlord break after 12 months on 13th December 2019.

The landlord has served a S21 notice to activate the break 13th December 2020 (landlord break after 12 months). I received this notice on 18th August 2020 before the new 6 month notice period was mandated by the government on 21st August 2020 where all notices after this date needs to be 6 months.

My confusion is should the landlord serve me a new S21 notice as the first notice they served was early because if you calculate 13th Dec 2020 (break term) this should have been served anytime before 12th September 2020 (3 months notice as required by govt) but the new rule came into effect 21st August 2020.

So my questions is does the landlord need to serve a 6 months notice as the first one was served early?

Thanks advanced for answering