Thanks for the update, Admin. I also queried DrayTek Support directly. The following "official" response is for others wanting an answer to the same question...

"Thanks for your email.

To download firmware and other utilities. The International ftp site
has the latest and previous versions of the firmware for the router
models and other devices.

The development team in the UK need to test and approve firmware to be
used, it does take a while to update on the website. We will pass on
on your comments to the appropriate team."

Of course, I suspected this to be the case, but more communication would be preferable. Leaving users blind has become par for the course with DrayTek recently. The feeling that you've discovered a great product, at an amazing price with brilliant support is definitely now a thing of the past. Inconstancies in support documents between sites is also of concern. There is a real sense of fragmentation across the DrayTek estate. Hopefully, this can be rectified in the not too distant future.

northerngit wrote: The development team in the UK need to test and approve firmware to be
used, it does take a while to update on the website. We will pass on
on your comments to the appropriate team

I do understand the needs for some regions of adapted settings (example mer - not many isp's worldwide using it etc) but is taking so long, by the time they will test or have ready the firmware at main draytek are out 2-3 other firmwares by now ... then when will test them? seems like a marathon for UK region
example:
2830n_sb_model at UK download pages is 3.6.4 ... at main draytek was 3.6.6 which disappeared the next day , then 3.6.6.1 and since yesterday 3.6.6.2 ... seems they are way behind