Purchased DONE5 ex-CAI (now an ex-DOH ticket) 13Dec16 from a TA on QF stock. Flew first leg on 24Aug17. Now looking to change some upcoming flights and turn into a DONE6. I understand that this change should be subject to historical pricing as of date of original ticket. I cannot get historical pricing on EF, does anyone here have access to the fare difference between a DONE5 and DONE6 ex-CAI on 13Dec16? Any help would be appreciated,