AA's tracking system is not like other airlines (I think DL has real-time tracking of miles based on when you board the aircraft using the BP reader) where miles post instantly.
Miles post in 2-4 days from flight (depends also on weekend and possibly departing location) for AA flights and varies widely for OW flights.
The 'Challenge' is not completed until the miles post.
To avoid the next question - 'I reach tier on the outbound' ... 'can I get the benefits on the return'.
Since the miles have not posted, the answer is no if in the case of the OP the trip is a MR with immediate turnaround (vs several days in destination city).
Also the completion of the Challenge may take a few more days for the new tier to hit the account as the program to check Challenges is not constantly run (may run once a week). This would further delay the OPs completion (in the computer) of the Challenge.
Since also the OP has may flights ticketed WAY beyond this Challenge, it would not hurt the OP to do the following:
1. Wait for PLT to hit their account (as evidenced by the information on aa.com for their account).
2. Call AA (the PLT line now) and indicate 'I am not PLT and these reservations were made when I had no status' and ask for them to be 'refreshed' with the new tier status. The reservation is created at a point in time and will stay based on that tier status. Tier status changes are not automatically updated to existing reservations. There have been reports that recently this may have been 'fixed' but a simple phone call really will insure that the new tier is in the PNR.
3. Go online to the newly refreshed reservations and assign yourself exit row seats or request upgrades to your heart's content.
4. Come on FT and update your signature to your new status. BTW, technically you should put that as PLT-Lite until you requalify in 2008 as a full-fledged flier.
If your next flight (not the MR on the same day) is scheduled prior to the PLT status truly 'hitting' your account, you can try calling in .. probably after the fact and get the bonus miles squared away.
Until your account reflects your status, you aint that tier.