Please note that although the tombstone says Solomon died in 1818, he was still very much alive in 1821.
Two documents have surfaced that state as much.

This tombstone was placed by the Sons of Confederate Veterans 15 - 20 years ago (in the 1990s).

A Clarke Co document dated 1821 Solomon's son refers to his father as "too old and infirmed" to represent himself regarding the stolen horses.∼The son of Jacob Strickland, Sr and Thamer Pitts of N.C. He married Amy Pace on Sept. 19, 1764 in Edgecombe Co, N.C. He served in the American Revolution as a PVT in both the Edgecombe Co, N.C. 1775-1777 and Nash Co, N.C. 1777-1783 Militia. His payment for his service is recorded in N.C. Revolutionary War Army Accounts Vol. 5, Page 37, Folio 3. He also swore the Oath of Allegiance to N.C. on May 31, 1780 and again on Nov. 16, 1782 when he entered land in Nash Co, N.C. Warrant Number: 256, BK. 57, p. 256 & Warrant Number: 452, BK. 57, p. 351. He also appears on the 1782 Nash Co, N.C. Tax list with 1,100 Acres of land, 2 Slaves, 5 Horses & Mules, and 50 head of cattle. He was paying taxes in Wilkes Co, and Franklin Co, GA by 1790. He was granted land by the State of Georgia in Wilkes Co. in 1791 BK. UUU, p. 282. He and his wife were charter members of Lystra Primitive Baptist Church in This land became Madison Co, GA. Members number Three and Four on Jan. 15, 1803. He removed to Jasper Co, GA by The association meeting for the year 1814. He is shown as being dismissed by letter in Sept. of 1817. His wife is shown as a dead member also in Sept. of 1817. His last known official transaction is on Nov. 5, 1821 when he was still attempting to collect for a horse and mare and two other horses, that had been stolen from him in Franklin Co, GA on Jun. 8, 1788 by Creek Indians. He had filed his claim in Wilkes Co, GA on Aug. 24, 1789. A Military Tombstone for him was in error placed at his son's Solomon's grave in Spalding Co, GA.
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Suggested edit: Solomon attested in Nov. 1821 regarding the horses that were stolen by creeks in 1788/9.
These are filed under his son - Ephraim.
Images - https://vault.georgiaarchives.org/digital/collection/FileIINames/id/67387/rec/69
-Page 2 shows his attestion.
-Page 3 - Ephraim indicates Solomon is old and infirm.

Jasper County Probate records.
https://www.familysearch.org/ark:/61903/3:1:3QS7-993Y-CVXS?i=148&wc=9SB8-7M3%3A267654901%2C267948801&cc=1999178
Solomon is indicated and old, and Amy is indicated as deceased 'last', (no date/year). Case regards the deed of gift made in 1804 to the children, and the children are suing Solomon Jr. who has the slaves and the children want the deed of gift honored as listed in 1804. The case includes the 1804 deed of gift. This was dated Oct. 31, 1818, and presented to court Nov. 11, 1818. The case is listed as to be reported settled Feb. 22, 1820.

However, in the court declarations minutes, this case is listed as settled and recorded July 5, 1821. This corresponds to the date listed in probate.
https://www.familysearch.org/ark:/61903/3:1:3Q9M-C3HS-J9VN-J?i=99&cat=126410

By this slave case, all we know is Solomon was alive in Nov. 1818, nothing more. I had assumed he was dead by the date in the probate file - July 5, 1821, however, the Indian claim disproves that.

By the indian case, we know he was still alive Nov. 11, 1821.
Contributor: Janice J (48336262) • [email protected]
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Suggested edit: This stone was placed in error, he and his son grave location are switched. Solomon SR wife Amy is buried at Concord Primitive Baptist Church in Jasper Co, GA.
Contributor: Lewie Dunn (47860774