The Inter-American Driving Permit (IADP) was created by Article XIII of the Convention on the Regulation of Inter-American Automotive Traffic, signed in 1943 by 21(?) countries in North, Central & South America.
As such, it pre-dates both the 1949 Geneva Convention on Road Traffic and the 1968 Vienna Convention on Road Traffic which implemented the more widely accepted International Driving Permit (IDP), and so for a period of time the IADP was the only international driving permit available.
Since the 1949 Convention regulates more than just driving permits it still remains in effect for other things, and since it has not been revised to remove the article which creates the driving permit, this permit still exists.
In general there doesn't appear to be any benefit to getting an IADP over the more widely accepted IDP, except for the following:
- Under the 1968 convention, Brazil does not recognize the IDP as valid for anyone under the age of 18 for any class of vehicle, or under 21 for vehicle classes C (vehicles exceeding 3500kg), D (vehicles used for the carriage of passengers and having more than 8 additional seats) & E (vehicle coupled to a trailer exceeding 750kg)
- Under the 1968 convention, possibly Honduras might not recognize the IDP for vehicle classes D & DE
- Under the 1949 convention, Guatemala "Will only permit that one trailer be drawn by a vehicle and will not permit articulated vehicles for the transport of passengers"
- Under the 1949 Convention, Jamaica won't allow you to drive for reward (operate a taxi, ride-share, etc), as well as the same restriction as Guatemala
1968 Convention Status
1949 Convention Status
Since it appears that none of the signatory countries to the 1943 Convention expressed any "Reservations" or "Declarations" as some did to the 1949 & 1968 Conventions the IADP might technically grant permission for some or all of the exclusions of the IDP.