William Bush and Mary Thetford's son John Bush and his wife Elizabeth Roach left Caldwell Co and were listed on the 1850 Jackson Co., Ill census. That data shows John Bush was born in SC in 1793 and is consistent with when we know his father William Bush was in Laurens County, SC.
Two of John and Elizabeth Bush's grown children migrated to Illinois with them and are also listed as heads of households next to their parents.
Listed next to these Bush members on the census is a William Thetford age 57 (b. 1793 in SC) and his wife, Lucretia age 47 (b. 1803 in NC). Lucretia's dates are consistent with her being the daughter of John and jemima Gately. Gately data shows that Lucretia Gately married a William Thetford and this census data would seem to back that up.
There is a handful of data strongly suggesting that the Bush/Thetford and Marcer/Gately families may have been related by the time the 3 Bush orphanswere bound out to John Gately in 1788-89 in Caswell Co.