I thought the only Xehanort that didn't time travel was Terra-nort? He came about when Ansem SoD and Xemnas was defeated (which is why Terra's body is allowed to stay in present time).
Master Xehanort, Young Xehanort, Ansem SoD and Xemnas all time travelled thanks to being in YX's personal time line
I never thought aside from a couple members it was particularly confusing, but I know it was for others. It's funny, the Re Mind DLC specifically has you sit through a slow scene where MX and Saix try to spell it out to Xigbar in order to make it more clear lol. I'll just list'em off.
Master Xehanort- Recompleted after the events of KH1 and KH2.
Ansem- Time travelled
Xemnas- Time travelled
Young Xehanort- Time travelled
Terra-Xehanort- Terra's body returning as part of his and MX's recompletion, but his Heart does not yet return. MX inserts time travelled Terra-Xehanort heart from BBS to control him.
Vanitas- Time travelled
Riku Replica- Time travelled
Xigbar- Recompleted then separated again by Xehanort
Saix- Recompleted then separated again by Xehanort
Vexen- Recompleted then separated again by Xehanort
Marluxia- Recompleted then separated again by Xehanort
Larxene- Recompleted then separated again by Xehanort
Luxord- Recompleted then separated again by Xehanort
Demyx- Recompleted then separated again by Xehanort
Xion- Reconstructed from Vexen's surviving research.