when the ff programs started, i would sign up for the plan if i flew the airline....i suggest you do this.....

you have the boarding passes for your prior flights, so you could ask for credit, however, the rules generally are you have to be a member of the program when the flight occurs.....some will let you sign up on board the flight & grt credit for it....

there are alliances of ff programs....if you look at an airline web site, it will show partner carriers which when flown, the ff mi can be credited to their program....the aa site will list ib, ba, etc.....be careful, because cheap fares often get reduced or no mi from a partner....

good luck...