Yup, they really did mention Carol had a fiancé in the pilot. Benton even tells Carter she’s dating an ortho guy (Taglieri, who shows up in this episode).
Now for some TV lore: Carol was actually supposed to die. She was billed only a special guest star, but the test audience loved her and latched onto that Doug/Carol history tease. The writers did a quick “never mind,” let her live, and the rest is history.
As for years/skills/competence—none of the main cast are attendings yet. Mark is Chief Resident (R4 but like the most trusted R4 in program), Doug would be just R4 but in pediatrics. Pitt analogy? Think Collins/Langdon level of competence. Susan and Peter are both R2s in ER and surgery (so, Mel/Cassie tier). Carter’s just an M3 med student, aka Victoria-level student-doctor.
The only actual attending we get is Morgenstern (William H. Macy), who’s both Chief of Surgery and head of the ER. Everyone else is basically a guest start parachuting in (Carson from cardio, Cvetic from psych etc.)
So yeah, we’re missing a “Dr. Robby” type actually supervising shifts. They fix that later once the characters grow and level into attendings themselves.
ER is iconic, but it did took some liberties ;)