Overlap or confusion in terminology describing predicates and complements?

[The source] is about the completers of thoughts, it is appropriate to include a brief description of complements. A complement (...) is any word or phrase that completes the sense of a subject, an object, or a verb. As you will see, the terminology describing predicates and complements can overlap and be a bit confusing. Students are probably wise to learn one set of terms, not both.

● A subject complement follows a linking verb; it is normally an adjective or a noun that renames or defines in some way the subject.
● Adjective complements = predicate adjectives.
● Noun complements = predicate nouns = predicate nominatives. See predicates, above.
● An object complement follows and modifies or refers to a direct object. It can be a noun or adjective or any word acting as a noun or adjective.
● A verb complement is a direct or indirect object of a verb. (See above.)

Comparing predicates vs complements, what else overlap[s] or is confusing? I simplified the exposition above and want to master both sets of terms (for predicates and complements).

The text in the link is titled "Predicates, Objects, Complements" and has three sections. When it gets to discuss complements, it simply states that predicates can sometimes be considered to be complements and vice versa. This means there is some overlapping in the definitions.

People who study grammar often want clear definitions that can lead to right/wrong decisions. With overlapping definitions, there may be more than one correct answer. This may lead to confusion.

Personally, I think natural languages (and English in particular) are too powerful to be covered by a finite set of rules (especially rules stated in a natural language...) Ambiguity is unavoidable; we should tolerate it.