The articles that are presented as "strict" and requiring immediate implementation are the first, the fifth and the sixth. The first is the one that most clearly related to principles of publicity ruling out secret reservations in the case of peace treaties. The 5th concerned the general rule of non-intervention in the constitution and government of other states and the 6th concerned dishonourable stratagems in times of war. The 6th article does relate to a publicity test though it is not primarily set out in terms of it whilst the 5th was found to be complicated both in including a mitigation and a mitigation of the mitigation.
The articles that would involve "latitude" in application and no necessary immediate action would be the second, third, and fourth, concerning the purchase of one state by another, the abolition of standing armies and the ruling out of national debt with regard to external affairs. The 3rd and 4th are the ones commonly thought to be out of date though I cast doubt on this assumption but the second on acquiring a state certainly could not be thought so.
The principle at work in Kant's distinction between the preliminary articles is between articles that require immediate implementation and ones that can be delayed though not indefinitely. The reason why delay can be given any room at all is not however clearly indicated with only one example treated as providing any reason at all. This is the example of the 2nd preliminary article on acquiring a state. Though such acquisition is not in accord with right there was a general public opinion which accepted it at the time says Kant. Even if this is correct it is unclear how it relates either to the article on standing armies or that on national debt. Further more, there is often support in public opinion for the use of the dishonourable stratagems of article 6 but this has not prevented Kant from placing these under the heading of "strict" articles.
It has to be said that this division of the articles is not handled in a way that either shows a serious ground for differential treatment of the specific requirements of the articles or why it is applied in the way it is. This account is perhaps one of the least satisfactory of the arguments in Perpetual Peace.