The frustrating thing is we have four places SJL may have meant to go: home (if, big if, it is true she planned tennis), the pub (for the diary), Shorrolds (if viewing was real), and apparently 123 Stevenage (if she really did drive straight there).
There are issues with all of them. DL is the source for the tennis thing and she's not reliable; no evidence was sought to establish if she ever turned up at the pub; nobody ID'd her at 37SR until after the police said that was her, and there's no evidence she went inside; and it doesn't look like she was at the wheel of her car when it was abandoned outside 123 SR, even though at the time sighted, she must have been.
The BW sighting is the tough one. The timing undermines all the others. As described, BW does indeed make it look like SJL was driving around at the behest of the unidentified passenger. But if this was under duress, why couldn't she just have just abandoned the car and bolted for it at the first red traffic light?
The evidence that there even was a crime is her friends' and family's conviction that she would never just disappear. That aside, she just vanished unwitnessed; there's no known crime scene except maybe her car, which has not been properly preserved as such.
We really are no further forward than at 10pm on 28/7/86.