There is no linking PNRs this is a myth. They will make a note to ref another pNR but when you have computers handling IROPS etc it really does not make a difference. The only time you get a link is you approach an agent together and they see you are group traveling together on an airline the employee hates working. Your hope is the agent actually cares about making someones day a little better because their day stinks and accomodate you as a group.