Thank you very much for taking the time.
"And the Lord appeared unto Abram, and said, Unto thy seed will I give this land: and there builded he an altar unto the Lord, who appeared unto him." - Gen 12:7 KJV
In Genesis 12, we see that "seed" is indeed singular and related to a promise. This fits in with Galatians 3 where it is stated that Christ is the sole seed of the promise.
"That in blessing I will bless thee, and in multiplying I will multiply thy seed as the stars of the heaven, and as the sand which is upon the sea shore; and thy seed shall possess the gate of his enemies;" - Gen 22:17 KJV
There are two seeds in Gen 22:17. I agree with your/W.Kelly's assessment that this is a multiple of seeds / seeds of flesh ussage in the first instance of seed in Gen 22:17. This passage lines up well with Romans 9:27.
"Esaias also crieth concerning Israel, Though the number of the children of Israel be as the sand of the sea, a remnant shall be saved:" - Romans 9:27 KJV
There is no explicit promise to the multiple seed in Gen 22:17, only that Abraham is promised to have a multitude of descendants. And of these descendants through Israel only a remnant is saved. The second seed in Gen 22:17 however very clearly lines up with Christ.
"I am the door: by me if any man enter in, he shall be saved, and shall go in and out, and find pasture." - John 10:9 KJV
"Wherefore Jesus also, that he might sanctify the people with his own blood, suffered without the gate." - Heb 13:13 KJV
"I am he that liveth, and was dead; and, behold, I am alive for evermore, Amen; and have the keys of hell and of death." - Rev 1:18 KJV
When we look at Gen 22:18, this also in reference to the singular seed that is Christ.
"And in thy seed shall all the nations of the earth be blessed; because thou hast obeyed my voice." - Gen 22:18 KJV
"Neither, because they are the seed of Abraham, are they all children: but, In Isaac shall thy seed be called. That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed." - Romans 9:7-8 KJV
"Now to Abraham and his seed were the promises made. He saith not, And to seeds, as of many; but as of one, And to thy seed, which is Christ." - Galatians 3:16 KJV
The seed of the promise (Christ) was called in Isaac's line (e.g. Matthew 1:1-25 KJV).
The seed is Christ, not Isaac.
"And the Lord shall make thee the head, and not the tail; and thou shalt be above only, and thou shalt not be beneath; if that thou hearken unto the commandments of the Lord thy God, which I command thee this day, to observe and to do them:" - Deut 28:13 KJV
The entirety of Deuteronomy 28 starts with an "IF" statement, and that "IF" statement is repeated in the line that talks about the tail and head.
The fact is that no one except for Christ fulfilled the law, therefore He is the only one that could be the recipient of the promises listed there. Christ is the head.
"For whosoever shall keep the whole law, and yet offend in one point, he is guilty of all." - James 2:10 KJV
"And kings shall be thy nursing fathers, and their queens thy nursing mothers: they shall bow down to thee with their face toward the earth, and lick up the dust of thy feet; and thou shalt know that I am the Lord: for they shall not be ashamed that wait for me." - Isaiah 49:23&26 KJV
This was addressed to the Israelites of the day.
I realize this is just a quoted section from William Kelly, but assuming you are advocating for the same position, are you proposing that Isaiah 49 contains a bestowed stewardship that is not continuous with Christ (who is of Israel) but is continuous with those of Israel that reject Christ?
If this is the case, why does it not apply to Christ? And why do you perceive it as a bestowed stewardship as opposed to a prophesy?
"For he that is dead is freed from sin." - Romans 6:7 KJV
The time-frame is an interesting question. I'm not terribly familiar with the context of the years. It sounds like a teachable moment and I would love to hear more on this.
I don't think anyone is making the claim that anything promised was voided or spoken falsely in scripture. The dispute is usually about what specifically was promised, how it was promised, and to whom it was promised.