Organic Soil Orders and 40 cm rule

I have a followup question on this topic: The lab manual says Of >= 60cm. Does this only apply when there is only Of horizon? And, as long as there is Om and/or Oh present with Of, the rule is total depth >= 40cm?

Yes, that is correct....... if only Of is present it should be thicker than 60 cm. But in APBI 200 course we would accept as a correct answer even if Of is thicker than just 40 cm.
And if two or three O horizons are present, they collectively need to be thicker than 40 cm
Things are actually much more complicated than this in the classification of Organic soil order, but for our Intro course, this will do.

Thank you!