I don't know if my case is different, but my eligibility period was until Oct 2021. On Oct 2021, I have received the response below.
Based on that, I suppose that it means the eligibility period is extended by one year, and if you get the remaining miles required to keep your status, you will do so for an additional 2 years. For Diamond, it would be 30K miles.
For your information, my eligibility period did get updated on the website to Oct 2022.
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Dear Customer,
Thank you for contacting Asiana Airlines.
For the convenience of Asiana Club members who are not able to use Asiana Airlines due to the prolonged Covid-19 impact, we will extend the qualification period by up to one year until 2021.
Therefore, if you are planning to maintain or demote your qualification based on the current eligibility period (2021-10-31), the eligibility period will be extended by an additional year to 2022-10-31.
For your Diamond grade maintenance, you need to accumulate 4,092 boarding mileages in this eligibility period.
If you have other inquiries, please do not hesitate to contact us again.
Thank you for your patronage of Asiana Airlines.
Sincerely,
Asiana Airlines, Asiana Club