User blog comment:YuutaScarlett/Another Anime Break?/@comment-25334245-20140826231856/@comment-1359322-20140827115541

Actually i think that was after the timeskip, Juvia only met Gray during the Phantom Lord Arc, and by the time for the Tenrou arc, Lucy only joined FT for 6 months, there was no way Juvia could've known Gray for 413 days back then. Well since the Tenrou group were frozen in time for 7 years, maybe Juvia didn't count those days.