Having worked at ABC and "Saga of the Big Valley" was one of 'our shows' we coordinated between production companies, advertising agencies & network .. as I recall, Eugene's character was not brought back because the story lines worked well with the characters who were always in it .. Peter, Breck, Linda Evans, Richard Long, Barbara Stanwyck, etc. .. there was so much to do with their characters that 'Eugene' was not needed and perhaps there was a contract problem as well . I do not really remember .. it was so long ago . most enjoyable show .. Usually, when you have many 'stars' in a series .. each is set to do X# out of total shows for the year .. back then we were doing a lot more than 22 shows a year as they do now and took less time to make them as well.. sometimes it comes down to money too .. but it also cost a lot less to film shows back then and 'stars' did not get anywhere near the money they make today ... thus less episodes and more commercials today!
