Nested が in the form Aが(Bが...)

Question

Please excuse me for not using the proper grammar jargons.

I am trying to parse the following sentence. (It is taken from this book. For this post it is crucial that I should not make a mistake copying the sentence. I triple-checked it.)

「〜した」が過去を表す場合はその出来事が今と関係がないことを表すことが多い。

その出来事が indicates that その出来事 is the subject corresponding to some predicate at some level. There are two possibilities as to what that predicate is.

1. The predicate corresponding to その出来事 is 表す. Locally the nesting of the sub-sentences looks like this: 出来事が((今と関係がない)こと)を表す. But this does not make sense.
2. The predicate corresponding to その出来事 is the sentence 今と関係がない. Locally the nesting of the sub-sentences looks like this: (出来事が(今と関係がない))ことを表す.

The second possibility makes sense, but is the syntax problematic? Japanese learners have probably all learned sentences of the form Aは(Bが...) like 彼は背が高い or 私は頭が痛い. But I do not recall textbooks etc. explicitly mentioning Aが(Bが...). Is this proper syntax?

Answer 1

I think it roughly goes something like this:

(「〜した」が過去を表す場合は)((((その出来事が(今と関係がない))ことを)表すことが)多い。)

Note that you should always partition sentences with wholesome 文節. 文節 = 1 自立語 + 0 or more 付属語. 助詞 falls under 付属語, so they should always follow the preceding 自立語. This may seem counter-intuitive to people familiar with European languages.

Your second suggestion looks good to me. No, there's nothing problematic about the syntax. For subordinate clauses and usage of は/が see these very informative answers:

は vs が in 私は言うように書いてください。

「は」vs 「が」 in subordinate clauses