Marketo smart list operators could get "knotty!"

Smart List operators, especially the less commonly used ones (e.g., "in past before", "in future after", etc.), could get tricky sometimes.

No doubt, it could get even the best of users wondering whether the set operator will qualify people they intend to qualify or not.

One crucial mechanical detail that not a lot of users know about is that when you use the "before" or "on or before" operators in a date field filter, the smart list will also include people who have an empty value in the respective date field.

This could be quite counter-intuitive, as a separate "is empty" operator is already available. But if you need to filter on people who have non-empty values only, then you'd need to use a separate filter with a "is not empty" operator along with the filter that has the "before" or "on or before" operator in it.

I always do a spot check of qualified people in the smart list, especially before running a campaign or flow step, to ensure I've filtered in the right people.

The last thing you'd need is to run a non-reversible flow step (e.g., "Send Email" step) on the wrong set of people.