The section you linked is largely out of date, so don’t rely on it. If exploring explicit representations (like ['d', N]), try to read the results of a formula column with type Any. For formulas, a single column may return any type of value, so if you construct a formula that returns various types (choices, choice lists, references, dates, etc), you’ll see a more realistic catalog of what’s possible.
Data columns, for all intents and purposes, are limited to their explicit type, or text to represent invalid values.