One thing I have picked up on is that you used to be able to renew 6 months early and the validity would continue to the end of this and add the 10 years.
Beware – if this has been done then your passport is only now valid for 10 years from the date of issue and the ‘extension’ won’t be recognised in the EU. I think this was picked up on and no early renewals get the extension, but there will be people out there that renewed years ago that maybe don’t realise they could have an issue in the future.
Or it’s something like that anyway.
I renewed just before first Brexit date, must be amongst the last to have EU on it.