If it was JC then these make sense, but it is a departure from what he did with SB. However, maybe with SB, things went down differently and he didn't have another premises to stash her in.
The fact that SJL has not been found after all these years is what puts me off believing it was JC. He seemed to incompetent and chaotic to pull something like that off. She was mixing with lots of men, some wealthy, plenty in her diary that were not bottomed out. Involved in some deal. A lot going on in her life that she compartmentalised and kept secret.
One of the things that unfailingly ticks me off about documentaries, articles and talking heads is how often they follow the official police line, that the SJL case was Cannan, because it "fits his MO". As you've noted, here and previously, er, what MO?
Pre-1986 he assaulted a woman in a phone box, he raped his wife, and he raped a woman in her shop;
Post-1986 he raped a woman in her car and attempted to force his way into another woman's car, presumably intending the same;
In 1988 he murdered SB, having previously scratched acquaintance with her (her widower recognised Cannan from hotel bars) and perhaps after a volitional extramarital fling, and dumped her body in a lonely place not far from a road.
Where's the MO in that?
Sometimes he is linked circumstantially to the Sandra Court case. If you buy that one for argument's sake, then his MO for disposing of bodies was to dump them in water, and when they're found, they're found.
Making an appointment, making her disappear without trace off the street and no evidence of his prior knowledge of her are all unseen in his only other known murder.
The only commonality I can see is around victim selection. DT was raped by Cannan in her car after she went out alone in the night following a row with her husband. SB was getting on badly with her husband whom she'd finally married after years together (you hear of people doing so because it was either that or split up, and they then wish they'd split up). SJL was in the process of splitting up with AL (whether he realised it or not).
The trouble with citing this as part of any MO is how did Cannan know this about his victims? He can't have; being in emotional upset, they may have inadvertently made themselves vulnerable to him, but he can't have planned around this.