Are you concluding that being "saved" and "believing" are one and the same thing?
Do you have any guesses, or do you know?
To me belief is only a part of salvation. I don't believe in "faith alone".
I believe repentance and obedience are also required. Do I have to power to live an obedient and repentant life on my own? No.
I believe it requires help from "the Helper". ( John 14:26; John 15:26; John 16:7; ) to live a Godly life. He doesn't force us to live Godly lives,
but He helps us live Godly lives if we let Him.
I don't know if you can be saved without the Holy Spirit (was Cornelius and his men saved before they got the Holy Spirit? or the disciples at Ephesus?).
But if it is possible, I believe it's very very difficult and next to impossible.
So it's back to "when" do we get the Holy Spirit? And how do you know if you have the Holy Spirit?
If you have a tangible gift (miracles, healing, tongues, etc..) then it's easy to know.
If you have the fruit then it might be possible to know, yet none of us bear good fruit 100% without crossing over the flesh occasionally.
I am pretty sure I could point out the fruit of the flesh in many of the people who frequently post here on TJ. (including myself sometimes).
So then... how do we know? In the Bible it was tongues, or fire above their heads, or doing miracles.
I have seen some of these things (tongues and miracles and prophecies) but I don't claim to have those particular gifts myself.
So how we know if we have received the Holy Spirit? Much less, how would we know if someone else has received Him?