Unfortunately the IAA like to use the word may which leaves things open to interpretation.
I spoke first hand to a contact at the IAA personnel licensing dept and he confirmed that applications received after 04/09 would still be processed with the intention of completion in 2021.
It seems some nations are treating it as applications not completed by 31/12 will be torn up, whilst others are honoring applications into 2021 as per the old regs.
My postal application was delivered to IAA on 04/09 (LOL) so it will be interesting to see if that counts as being received. EASA continuity will likely not be an issue for me so I am not too bothered if the deadline was missed and the licence turns up sometime in Q1 2021. Again this is based on my interpretation of the text and what I received from IAA contact.