I beg to differ.

Canaan announced the A721 on 2016-11-07. Commit 04e6a4b, titled Add Avalon7 support, was committed by qinfengling on 2016-07-29 and published by Canaan in the avalon7-dev branch of their cgminer repository on 2016-11-05. In other words, Canaan published the source code for the A721's version of cgminer two days before they officially announced the miner.

Canaan announced the A821 on 2017-12-20 at the latest. Commit 6786bbd, titled Add Avalon8 support, was committed by qinfengling on 2017-09-11 and published by Canaan in the avalon8 branch of their cgminer repository on 2017-09-27. In other words, Canaan published the source code for the A821's version of cgminer roughly three months before they officially announced the miner.

Canaan announced the A921 on 2018-09-19 at the latest. Commit fbc869b, titled Add Avalon921 support, was committed by Johnson-Fan on 2018-09-10 and published by Canaan in the avalon9 branch of their cgminer repository on 2018-09-11. In other words, Canaan published the source code for the A921's version of cgminer roughly eight days before they officially announced the miner.

Canaan announced the A10 at 2019-03-28T15:21Z. It is now almost seven months since the official announcement and there is still no published source code for the A10 in any of their GitHub repositories at the time of writing. The only entry for the A10 to date is the avalon10-docs repository, which merely contains a manual for the A10's API.