The suspicious looking guy enters the Texas Theatre. Does Brewer need to see this guy actually enter the door to know he has entered the building?
Yes.
Even though Postal doesn't see Oswald enter the theatre, she does provide us with the information that Oswald never passed her position as she was looking west, up Jefferson.
Walking past Postal isn’t the only other option. The man could have done an about face. He could have crossed the street. He could have gone down the alley separating the theater from the furniture store.
Postal was stood on the sidewalk just in front of the Box Office, checking out the police cars blaring by. She actually sees Oswald approaching from the east but then she turns to look west and doesn't see him ducking into the theatre:
That’s what she claimed, but when Brewer asked her if she sold a ticket to “that man” she said “what man?”. By the way, she never said anything about it being Oswald.
Also, if Brewer really “knew” that man entered the theater without buying a ticket then why ask Postal at all if she sold him a ticket? And why would she say she wasn’t sure? None of this fits together.
Brewer's account of following Oswald into the Texas Theater is confirmed by both Postal and Burroughs
Bull. How does not seeing someone enter confirm when somebody entered?
"I don't know if this is the man they want," I said, "in there, but he is running from them for some reason,"
Postal saw nothing that would suggest that anybody in the theater was “running” from the police.
Brewer's account of what happened seems completely credible and is corroborated by multiple witnesses
Brewer’s account of when and how Oswald entered the theater is corroborated by nothing and nobody. And it is contradicted by Burroughs and Davis.
and there is no doubt in Brewer's mind that the man he saw outside his shop and who ducked into the Texas Theater was the man he pointed out to police and who was subsequently arrested in the cinema - Lee Harvey Oswald.
When did Brewer ever say there was no doubt in his mind?