I never saw anything about spiritual jurisprudence regarding Wills and Testaments in the scriptures.
Notice to whom Hebrews is written:
Heb 1:1,
On many past occasions and in many different ways, God spoke to our fathers through the prophets.
The fathers are Jews and God never spoke through the prophets to the Gentiles and the church wasn't even around then.
The only other place that mentions a New Covenant is Jeremiah, another book written to Israel. Could it be that Hebrews, a book written to Jews is referring to Jeremiah, another book written to Jews? Furthermore, if you read all of Jeremiah 31 it is obvious none of it has come to pass.
All the other verses mentioned promises, but a promise is not a covenant.
Hebrews 9
15 And for this cause he is the
mediator of the new testament, that
by means of death, for the redemption of the transgressions that were under the first testament, they which are called might receive the promise of eternal inheritance.
16 For where a testament is, there must also of necessity be the
death of the testator.
17 For a
testament is of force after men are dead: otherwise it is of no strength at all while the testator liveth.
Hebrews 10
9 Then said he, Lo, I come to do thy will, O God. He
taketh away the first, that he may establish the second.
Hebrews 8
13 In that he saith, A
new covenant, he hath
made the first old. Now that which decayeth and waxeth old is ready to
vanish away.
Those verses describe the legal terms, conditions, and characteristics, aka jurisprudence, of a Will and Testament.
Those in Christ are heirs of the promises of the New Will and Testament.
But not those who do not believe such, and demand to opt out.
If you read Hebrews 8:6-13, most of which is an essentially verbatim quote from Jeremiah 31, it is obvious that it has all come to pass.
It begins with:
6 But
now hath he
obtained a more excellent ministry, by how much also he
is the mediator of a better covenant, which
was established upon better promises.
It ends with:
13 In that he saith, A new covenant, he
hath made the first old. Now that which
decayeth and
waxeth old is ready to vanish away.
Notice the tenses. They are exclusively past and present. Not one future tense to be seen.
That's complete fulfillment.