The rule arises from article six of the Schengen Borders Code:
Article 6
Entry conditions for third-country nationals
For intended stays on the territory of the Member States of a duration of no more than 90 days in any 180-day period, which entails considering the 180-day period preceding each day of stay, the entry conditions for third-country nationals shall be the following:
(a) they are in possession of a valid travel document entitling the holder to cross the border satisfying the following criteria:
(i) its validity shall extend at least three months after the intended date of departure from the territory of the Member States. In a justified case of emergency, this obligation may be waived
(ii) it shall have been issued within the previous 10 years;
This means that a third-country national cannot enter the Schengen area more than ten years after the issue of the passport, even if the passport is not yet expired. It does not mean that passports valid for longer than ten years are unacceptable.
My understanding of the rule is that the extra months beyond ten years are not counted when applying the six month validity rule. Hence your passport which had a ten years 3 months validity when issued should be viewed as expiring on 27/03/22 instead of 27/06/22.
Thus it has more than six months of validity remaining so you are fine.
SHUT OUT Brexit passport warning for millions of Brits – renew today or risk No Deal EU travel ban
Those with less than 15 months left on their passports could be at
risk if they plan to travel after March 29 – find out if you’re
affected
The UK Government has posted Advice for British passport holders if the UK leaves the EU without a deal
After 29 March 2019:
You should have at least 6 months left on your passport from your date of arrival. This applies to adult and child passports.
If you renewed a passport before it expired, up to 9 extra months may have been added to your new passport’s expiry date. Any extra months on your passport over 10 years may not count towards the 6 months that should be remaining for travel to most countries in Europe.
The new rules will apply to passports issued by the UK, Gibraltar, Guernsey, the Isle of Man and Jersey."
Credit:stackoverflow.com‘