The average man marries first at the age of 23.  If Isaac was Jabez's first child, that would place Jabez's birthyear around 1766, not 1774.  And if not ca. 1766, then he was more likely born earlier, rather than later.

If Isaac really was born in 1790, and evidence supports that he was, it is highly unlikely that Sarah was born in 1776.  The average woman marries first at the age of 19, which would place her birthyear at around 1770.  On the other hand, if she is a second or third wife of Jabez and not Isaac's mother, then it's plausible she was born in 1776.

1.  Marriage Record:

2.  1790 Census Index/Images (online at Ancestry.com, Image #2 of 10; extracted by Diana Gale Matthiesen):

1790

NY

Dutchess Co.

Pawling

Roll 6

p. 38

Ln. 15/41

Jabez Corbin

1-2-1-0-0

These data indicate:

Gender and Type	Age Class	Therefore Born	Individuals Inferred
1 free white male	16 or over	in or bef. 1774	= Jabez
2 free white males	15 or under	1774-1790	= Son A = Isaac (b. 1790)
1 free white female	all ages	in or bef. 1790	= Sarah

Jabez clearly married well before 1794, which he would have had to have done if he has a son born in 1790.  In fact, given that Isaac was born in November, he was probably born after the enumeration of the census, which would make him Jabez's third child, not his first.  There are six other CORBIN households in the county, four of them in Pawling.

3.  1800 Census Index/Images (online at Ancestry.com, Image #X; extracted by Diana Gale Matthiesen):

1800

-

- Co.

- Twp.

Roll -

p. -

Ln. -

-

-

-

These data indicate:

.  Rev. Harvey M. Lawson, compiler.  1905.  Descendants of Clement Corbin of Muddy River (Brookline, Ma. and Woodstock, Ct): with notices of other lines of Corbins.  Hartford Press, Hartford, CT (online at Ancestry.com and GoogleBooks):

p. 329

JABUS or JABEZ CORBIN, said to have come from Long Island, lived at Quaker Hill, in the town of Pawling, Dutchess Co., N.Y.  He m. Sarah Lawrence (or Mary Geeseman or Lucy Cheeseman).  Sarah Corbin is buried at Fishkill, N.Y.  She was b. in 1776, at Lawrenceville, L.I.  He was b. about 1774, and m. in 1794. Children: i.   ISAAC.  (See later.)   ii.   BENJAMIN, was a farmer in Penn.   iii.   TALLMAN, went to Penn.   iv.   GEORGE, lived in Sherman, Conn., where he was a carpenter; one dau. m. _____ Sperry, another m. _____ Ballard, and a son, George, resides at Brookfield, Conn.

p. 330

v.   THOMAS, lived near Fishkill, N.Y., and had two sons, John and Isaac.   vi.   WILLIAM.  (See later.)   vii.   LAWRENCE, lived in Putnam Co., N.Y.; a son, Thomas, had a dau., Amanda, who resides at Newburgh, N.Y., and a dau., Elizabeth, who m. _____ Thorpe, and lives at Brewster, N.Y.   viii.   SARAH, m. Harry Case of Mattawan, N.Y. ...

I can find no such place as "Lawrenceville" on Long Island, NY.  There is a "Lawrence" in Nassau County, which is on Long Island.

.  Public Member Trees (online at Ancestry.com).