So Month is not performing as you might expect it to here - you are looking at - has a month elapsed since March 31st. Let's pretend the date was the 15th - not the 31st. Would you say that April 14th is one month after March 15th? No - you would say that April 15th is one month later. Let's extend this logic to March. Without any external knowledge - one would expect the the one month mark at the impossible April 31st. Applying the same logic - Alteryx says April 30th is not one month later. It is 30 days later. It is the last day of April - but it is not one month later. Perhaps you want to look at Month vs Month instead of Day vs Day? Or compare last day to last day? Alteryx discusses this in the notes on datetime:
