The honest answer is that nobody knows, and that the question may not have an answer.
A layout too simple to have an inventor
Three cards in a row is not a design so much as the obvious next step after one card. It appears in card reading practice without a traceable first publication, and any claim that a named figure devised it should be treated with suspicion unless a source is produced.
This atlas therefore records the layout and its common position meanings, and records the authorship as unknown rather than filling the space with a plausible name.
The assignment is the variable, not the count
What varies between readers is not the three cards but what the positions are taken to mean. Past, present and future is the commonest assignment and by no means the only one: situation, action and outcome; you, the other, the relationship; mind, body and spirit; and the plain instruction to decide before dealing. The atlas records the common assignment in the layout and treats the others as equally legitimate.
Why that matters
A spread does not know what its positions mean. The meaning is a rule the reader brings, and it is fixed before the cards are turned or it is not fixed at all. A reader who decides after seeing the cards which position was the future has removed the only constraint the layout provided.