To make it super clear that there is no crossover you could simply avoid games by those 4 players covered by Oleksiyenko. There should still be more than enough source material from the old masters.
Another point of difference would be to organise your puzzles by theme as opposed to organising by player as Oleksiyenko does. I feel quite strongly that solving puzzles organised by theme is the best way to build pattern recognition which is what most adult improvers need. The more specific the themes, the better.
Note that your course idea is somewhat similar to this existing course:
https://www.chessable.com/world-champion-calculation-training-part-1-steinitz-lasker-capablanca-alekhine/course/67775/ by GM Oleksiyenko. (There are parts 2 & 3 too, covering later world champions).
This course (https://www.chessable.com/don-t-panic-a-chess-master-s-guide-to-calculation/course/81621/) also features the (very) old masters but I think a lot of is composed puzzles so probably less relevant.
To make it super clear that there is no crossover you could simply avoid games by those 4 players covered by Oleksiyenko. There should still be more than enough source material from the old masters.
Another point of difference would be to organise your puzzles by theme as opposed to organising by player as Oleksiyenko does. I feel quite strongly that solving puzzles organised by theme is the best way to build pattern recognition which is what most adult improvers need. The more specific the themes, the better.
Best of luck with creating your course!
Oh, thanks for mentioning that! Will definitely make some adjustments then 😬
Great idea for a Chessable course Martin!
Glad you like the idea 😀