had needs to logically indicate a time period that is before/prior to another PAST period.

in 1: he limousine driver waited before deciding that his client is not going to turn up.

the time reference here is present tence, so a simple past tense to indicate sufficient.
if the sentence had been: ...that his client WAS not... then I think "had" would be required.

in 2: Couples that were married or engaged at the time of survey "had" lived together before making a final commitment...

clearly the time reference is in the past, so the logical sequence is: couples lived together, couples got married/engaged, couples took the survey. to properly express that the couples' living together is the furthest past of all 3, use had.