On further thought, your question is not a duplicate
Let's say I craft a Page of Limited Wish [...] Would this allow me to cast Limited Wish? I have a spell slot of the appropriate level (higher, even), and I have the page to make the spell "known" to me.
And the supposed dupe asks:
Can Xylitol cast 1st level spells using the bonus slots for his 2nd, 3rd, and 4th level spells?
You ask about casting a spell you don't even know, by using a magic item and whether this is a way to use high-level spell slots. The other question asks about upcasting spells they do know, without using a magic item, and whether this is a way to use high-level spell slots.
Both questions make the same incorrect assumption but are asking about different things. To look at it another way, if the assumption that you can have bonus spell slots that are above your usual level was correct, these questions would be, at least to some extent, different questions. Just because they made the same wrong assumption does not mean they ask the same thing.
I will say that even if these are not duplicates they are very similar questions. I believe my descriptions of them above show just how similar they are, but they are nonetheless, asking different things.
That said, duplicates are actually helpful
When question A is closed as a duplicate of question B, this increases the number of ways people can find the answer to question A/B. It means the Google and site searches have both been improved, sometimes dramatically.
So there is nothing wrong with posting a question that is marked as a duplicate, it just means you didn't find it, and I can tell you, none of us can find everything. In fact, I regularly upvote question that are closed as duplicates that were not alarmingly easy to find (like a near-exact title match) because the question is still a good question.
In terms of actually finding a duplicate, they can be looked for in primarily three ways: An Internet search, the auto-generated suggested list, and, what I use the most, site search with tags and keywords. For example this search or this search, (where the second works only because I just added the spell-slots tag to that question). Site searching is difficult and imperfect, and sometimes your favorite internet browser just knows much better.