Of course it's documented; I'm guessing you got someone on the phone who wasn't very knowledgeable about FSS, not a Premium Services agent. The link to the FSS page on aa.com is shown in the wikipost at the top of the page.

Services include:

Connection assistance

You'll be greeted upon arrival and escorted to your next flight. If you have time, we’ll accompany you to the Admirals Club lounge (where available).

Includes:

• Arrival gate meet and greet
• Admirals Club lounge access
• Priority re-accommodation during delays
• Gate escort
• Assistance with connections on other airlines
• Early boarding

Arrival assistance

Upon arrival, we’ll meet you at the gate and escort you through Customs and Immigration and/or baggage claim.

Includes:

• Arrival gate meet and greet
• Car service coordination
• Escort through Customs and Immigration for international arrivals
• Admirals Club lounge access**
• Escort to Baggage Claim
• Luggage retrieval
• Escort to car service

*Five Star Service does not include continuous care, medical assistance, dispensing medication, assistance with meals or aid within a restroom. Contact Reservations at 800-433-7300 for help with these needs.

**Admirals Club lounge access not available on international arrivals.

Flagship Lounge would only be included for those who can access via class of service or status. (Note: I'm posting my experience over the times I've used FSS, several times in the last six months alone.)