An excellent observation. We forget the continuity issues which arose in Lorimar Dallas on occasion and re-casting characters, most notably Gary Ewing, Jenna Wade and Kristin Shephard. Funny how we readily accepted the changes in actors with those roles but not Miss Ellie. I suspect we were a little more forgiving only because those other characters were not as embedded into the series like Miss Ellie was. It's also worth mentioning how forgiving we were with those continuity changes in Lorimar Dallas but not when the writers of TNT Dallas attempted the same.
We're a strange mob sometimes.
The change in Miss Ellie was the only time that an actor playing someone from the main cast was changed. Miss Ellie was a huge character in Dallas during those first 7 seasons DVD, sticking strongly in people's minds as this tough as nails, yet caring, ranch woman. Then in comes Donna Reed in Season 8 DVD, playing Miss Ellie very differently, as a glitzy oil baron's wife with a much softer character. It was a real shock to the system, and too much for some fans.
David Ackroyd played Gary Ewing for 2 episodes, but then it was over a year before Gary was seen again played by Ted Shackelford, and then Knots Landing began with Ted Shackelford as Gary. Colleen Camp played Kristin Shephard for 2 epsiodes in Season 2, but the memory of Camp's Kristin is hardly striking. I mostly remember her for making moves on Bobby in one of her episodes. Mary Crosby's Kristin Shephard was a regular in Season 3 and stood out, being somewhat deeper in character and well into J.R.'s devious world.
Morgan Fairchild played Jenna Wade for 1 episode in Season 2, as this devious, spoilt minx, where Charlie was explained as not being Bobby's daughter. Francine Tacker played Jenna Wade for 2 episodes in Season 3, as this ultra-confident woman with very high self-esteem, and it had been over a year since Fairchild's Jenna made her one appearance. Tacker's Jenna is someone with a firm control of her life, and even gives Pam a piece of her mind regarding Bobby. Tacker's Jenna had taken control of her situation with Renaldo, and got him and Charlie on good terms as father-daughter. Priscilla Presley played Jenna Wade as a regular from Seasons 7-11, initially playing her very well as a woman who is making do in a bar job yet is fiercely proud and independent. Yet in Season 8, all the old storylines about Charlie's father and Renaldo now being a stranger to Charlie and on bad terms with Jenna, come to the fore, contradicting past events and making it drag on for much longer. Presley's performance as Jenna was nowhere near as good from Seasons 8-11.
David Wayne played Digger Barnes in the first two seasons DVD, but only appeared in about 4 episodes in total, while Keenan Wynn's Digger Barnes was a semi regular but not a part of the main cast. Apart from Miss Ellie, the recasting of Digger Barnes is probably the most high profile recast, but I think it worked well. Wayne showed us Digger's very bitter side and also his attempt to reconcile with Jock for the sake of Bobby and Pam at the first Barbecue, only for Jock to soon throw it back in his face. On the other hand, Wynn's Digger is more resigned to having lost the war and is caring about his family more, with the occasional hint of bitterness at Jock, but Cliff is worse with the anti-Ewing feeling than Digger by this time, which Digger has a go at Cliff for in one episode. Cliff was more bitter because he had J.R. as his rival, somebody without any pity or empathy for his arch rival whatsoever. J.R. and Cliff were always enemies. On the other hand, I think Jock always had a certain sentiment for the days when he and Digger were friends and regretted the path that Digger had chosen.