So just to be clear, you have brought up 2 issues:
The bad date code switches
Inability to update the firmware
The bad date code switches have a wiring defect which impacted the range of the wireless signal. Flashing to a new firmware will not resolve that. But since those switches are joined to your network, it sounds as if you don’t have to worry about the signal issue.
The harness will only solve the inability to upgrade firmware. That’s due to an older bootloader. Upgrading the firmware via the harness will replace the bootloader and you’ll be able to OTA firmware going forward.
I was sent the wiring harness, I ended up doing any switch that started with 22 on the sticker, didnt matter if it was 2208, 2209, 2212, I did them all, in total 23 switches. I am happy to say this resolved all my issues and I now have 3.04 on all of them.
If you need to do this it is fairly easily to flash these and only takes about 30 second in total, other than having to remove the device and put it back in.
There are two basic steps, 1st wipes out the firmware, 2nd loads v2.0.
For anyone doing this, after you flash.
Install the dimmer with the airgap out
For me I was on hubitat so I started the ZigBee pairing, then push in the airgap
Once it was discovered I clicked on it which took me to the device page.
From the Command Page, I clicked refresh then Config, then refreshed by browser. You should see version 2.0 in the state box.
I would open another window in hubitat that shows the logs and other from the same Command tab, then clicked UPDATE FIRMWARE and watched it update in the logs.
The switch LEDS should go green for along time, when they go back to CYAN or Blue when it is completed.
From the Command tab in Hubitat, I then hit Refresh, Configure and refreshed the browser. You should now have v 3.04 in the state box.