For Cycle 3, the IRS required that the plan document explicitly specify the determination period for calculating matching contributions, including safe harbor match. Take a look at item C.18 in the adoption agreement.
If the adoption agreement says the determination period is annual, and the employer calculates and deposits the match each pay period, then a true-up will be required. If the adoption agreement says the determination period is per pay period, then a true up would not be allowed unless the plan were amended, and then the rules for mid-year changes to safe harbor plans would come into play.
If memory serves me right, FT had a FAQ sheet about this back when Cycle 3 came out. It is probably still on their website somewhere. Or I'm sure they would be happy to send it to you if you contact them, as Bill suggested.