I could not fined any answer to this particular question on wowhead.
So I counted all my reps I have 97 Exalted on this toon.
I did not count:
Argent Dawn. Was exalted but no loner are (currently at war with because I hate the light lol)
Aldor + Scryers. Both have been exalted for the FoS but in the middle of changing back to Aldor. Forgot to buy the BS patterns
Frenzyheart + Oracles. Oracles was Exalted working on Frenzyheart now.
Odd my Achievement says 98 reps even tho I counted more then once I have 97. Now to my understanding Aldor + Scryers count as just 1 being they are opposite factions same for Frenzyheart + Oracles.
Going by my count the 3 I did not count should give me 100.
Do I need to have the reputations all at exalted for them to count for this achiev?, and going back to Aldor and now working on Frenzy is what is screwing me over and hating on the Argents?.