Did anyone notice that in the scene where Sheliah,Darrin's old girlfriend,came to MacMahan and Tate,the entrance to the office where Darrin worked was different than in all the rest of the episodes-By this,I mean the entrance was just a door,with a sign on it,and and did not have its'traditional engraving?

Yes it was different and Darrin had a young secretary called Helen who I don't think appeared as a secretary at McMann and Tate again after the pilot.From then on it was always "Betty" played by a number of actresses. Also between the pilot episode and the episode "Snob in the Grass" Sheila's house also totally changed but that was a few seasons/years later and Sheila of course could have moved in that time I guess.

Did anyone notice that in the scene where Sheliah,Darrin's old girlfriend,came to MacMahan and Tate,the entrance to the office where Darrin worked was different than in all the rest of the episodes-By this,I mean the entrance was just a door,with a sign on it,and and did not have its'traditional engraving?

Yeah, they had different sets in the pilot episode than they did later. You may have already noticed that the sign outside Darrin's office says "Vice-President" and not "Account Executive" like it would for the remainder of the series.