Does a subject “it” refer to the preceding subject or preceding object if bo...

In a technical text, I once wrote a sentence similar to the following one:

As the aforementioned notion of the maximal doodad is based on the long thingum, this notion targets extended hickeys, such as whatsits or gizmos.

Here, the long thingum, the maximal doodad, extended hickeys, whatsits, and gizmos refer to some technical concepts irrelevant and not explainable here.

My English proofreader (whom I cannot ask any longer) corrected this to

As the aforementioned notion of the maximal doodad is based on the long thingum, it targets extended hickeys, such as whatsits or gizmos.

Purely grammatically speaking, does “it” refer to the subject of the preceding subordinate clause (the subject “the above notion of the maximal doodad”) or to object of the preceding subordinate clause (the object “the long thingum”)? Or is the English grammar silent about this and the antecedent of “it” is ambiguous?

As a matter of grammar, a pronoun refers to a noun, usually a preceding noun. There is no grammatical rule that specifies which noun a pronoun refers to.

However, as a matter of writing clearly, it is recommended that a pronoun refer to the immediately preceding noun unless the context makes clear that the pronoun can logically apply only to some other noun.

Now, because your use of nonsense words means that we have no clue about context, my feeling is that your repeating “this notion” avoids any ambiguity. However, is it really the notion or the maximal doodad itself that targets extended hickeys? This may have been the reason your proofreader replaced “this notion.”

Assuming it is maximal doodads that target extended hickeys rather than a notion, you can make the sentence concise without any chance of ambiguity with

Because the long thingum is the basis of maximal doodads, they target extended hickeys …

In short, it avoids ambiguity to put a pronoun close to the noun it refers to, but context may permit you some flexibility.