I agree with attempting to leave no red flags, but our Jimmy and his accomplices have the checking regime down remember. They will have an idea of the time scales. If Jimmy exists.
The time scales were on a knife edge.
My impression is that Kate and Gerry's visits were at regular timed intervals and therefore easy for Jimmy the Abductor to factor in to his or her plan.
But Jimmy the Abductor would have noticed the more erratic movements of the other two couples with no precise measurement of timings between visits. That irregularity was no doubt factored into Jimmy the Abductor's strategy, because it was a very high risk strategy.
For example ... had Jes not stopped to speak with Gerry ... there is a high probability he would have had a face to face encounter with Jimmy the Abductor leaving 5A grounds.
Subsequently in combination with Jane's description ... that might have been enough to lead directly to him and to Madeleine.