Listed in one source as the 10th Earl of Darnley, which may have resulted in the confusion.
https://archive.org/details/scotspeeragefoun05paul/page/348/mode/2u...
https://en.wikipedia.org/wiki/John_Stewart,_1st_Earl_of_Lennox
https://en.wikipedia.org/wiki/Earl_of_Lennox
https://www.wikitree.com/wiki/Stewart-1338
https://ancestors.familysearch.org/en/LBC2-D1R/sir-john-stewart%2C-...