Hi, I have to say you got some wrong information about the series here. The main author was Richard Carpenter, he created the series. Later on there were some other authors but they only did a few episodes.
The first director who did most of the series (I think complete series 1) was Ian Sharp who created the distinct look of Robin of Sherwood.
Clannad did indeed see some of the material and they read the scrips. I know this for sure because Richard Carpenter told it on a Con in England last year.
I think this is a masterpiece of Television-Entertainment, because it has great characters and cast, good costumes and great story lines. For me still one of the best TV-series ever!