Again, I'm sorry, but, in reality, you "know" no such thing. For starters, the word "given" doesn't even appear in the original Greek (check it for yourself, please). No, it was added by the translators and for this reason it appears as an italicized word:
"In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink. He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water. (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified)." (John 7:37-39)
Also, that the Holy Ghost WAS ALREADY GIVEN, in certain aspects, is quite obvious in that people in the Old Testament either had the Holy Spirit IN THEM or UPON THEM or both...even as we've both cited verses which prove the same. With such a reality before us, what was Jesus actually saying here in John 7:37-39? Well, when He said, "If any man thirst, let him come unto me, and drink", this immediately conjures up images of what transpired with the children of Israel during their wilderness journeys when they "thirsted".
You may recall the following:
Exodus chapter 17
[1] And all the congregation of the children of Israel journeyed from the wilderness of Sin, after their journeys, according to the commandment of the LORD, and pitched in Rephidim: and there was no water for the people to drink.
[2] Wherefore the people did chide with Moses, and said, Give us water that we may drink. And Moses said unto them, Why chide ye with me? wherefore do ye tempt the LORD?
[3] And the people thirsted there for water; and the people murmured against Moses, and said, Wherefore is this that thou hast brought us up out of Egypt, to kill us and our children and our cattle with thirst?
[4] And Moses cried unto the LORD, saying, What shall I do unto this people? they be almost ready to stone me.
[5] And the LORD said unto Moses, Go on before the people, and take with thee of the elders of Israel; and thy rod, wherewith thou smotest the river, take in thine hand, and go.
[6] Behold, I will stand before thee there upon the rock in Horeb; and thou shalt smite the rock, and there shall come water out of it, that the people may drink. And Moses did so in the sight of the elders of Israel.
[7] And he called the name of the place Massah, and Meribah, because of the chiding of the children of Israel, and because they tempted the LORD, saying, Is the LORD among us, or not?
In his first epistle to the Corinthians, the Apostle Paul tells us that this "Rock which followed them was CHRIST":
I Corinthians chapter 10
[1] Moreover, brethren, I would not that ye should be ignorant, how that all our fathers were under the cloud, and all passed through the sea;
[2] And were all baptized unto Moses in the cloud and in the sea;
[3] And did all eat the same spiritual meat;
[4] And did all drink the same spiritual drink: for they drank of that spiritual Rock that followed them: and that Rock was Christ.
Yes, when God instructed Moses to "smite the rock and there shall come water out of it that the people may drink", in type, this was Christ being "smitten" and the water was representative of the outpouring of the Spirit. Jesus more than likely was alluding to this very event when He told His hearers:
"In the last day, that great day of the feast, Jesus stood and cried, saying, If any man thirst, let him come unto me, and drink. He that believeth on me, as the scripture hath said, out of his belly shall flow rivers of living water. (But this spake he of the Spirit, which they that believe on him should receive: for the Holy Ghost was not yet given; because that Jesus was not yet glorified)." (John 7:37-39)
IOW, in the same manner in which the outpouring of the Spirit (which was typified by the water) didn't come until AFTER the rock was smitten, so, too, there wouldn't be the outpouring of the Spirit on the day of Pentecost until AFTER Christ, the "Rock", had been similarly "smitten". IOW, Jesus was specifically talking about the outpouring of the Spirit on the day of Pentecost and He was NOT saying that "the Spirit hadn't been GIVEN" in any manner until or prior to this specific point in time. Again, we have ample examples of believers in the Old Testament who either had the Spirit IN THEM or UPON THEM.