The key difference being that at the Fifth Congress both were seen as important but at the Sixth there was a marked tendency to reject any minimal demands as bring operative in the short term.
Crucially, the Sixth Congress also saw the adoption of a programme by the Comintern which was more in line with maximum demands than with transitional slogans.
[1] Transitional demands differ from calls for reform (a minimum programme) in that they call for things that governments and corporations are unwilling or unable to offer, and therefore, any progress towards obtaining a transitional demand is likely to weaken capitalism and strengthen the hand of the working class.
So "Rule by workers' councils" would not be a transitional demand, as it would imply the overthrow of capitalism.
The BBC television documentary Lefties, which aired in several parts in April 2006, featured interviews with people who were radicals in the 1970s and 1980s, in which the concept of transitional demands is described.