When Did Problems Start In The Polesotechnic League?

See here.

Very approximately:

the Polesotechnic League was founded some time in the twenty third century;
the Council of Hiawatha was held at the end of that century;
the Mirkheim crisis was a hundred years later, when Nicholas van Rijn was eighty;
the first van Rijn story, "Margin of Profit," is set perhaps forty years earlier? - although, in that story, van Rijn thinks of himself as "...aging..." (The Van Rijn Method, p. 147);
thus, "Margin of Profit" is set perhaps a hundred years after the founding of the League?

Five major problems in the League were:

(i) cartels;
(ii) oppression of primitive races;
(iii) the plight of races lacking the capital to enter Technic civilization;
(iv) Merseian resentment of that civilization;
(v) unscrupulous traders arming backward races.

(i)-(iv) were well developed by the time of the Mirkheim crisis but (v) was already happening in "Margin of Profit." I think of the first nine installments of Poul Anderson's History of Technic Civilization as "the Rise of the Polesotechnic League" and the second nine as its Decline. The "Rise" is so called because it includes three pre-League stories, one story about Adzel as a student, one about Falkayn as an apprentice, another about Falkayn as a journeyman and two about van Rijn maybe "aging" but not yet as old as in Mirkheim!

However, the real Rise period was before the Council of Hiawatha, thus before van Rijn's birth, and unfortunately, there are no stories set in that period.