In 1920 she was listed twice, once with her parents and once with her husband.

There may have been another Emma McCarty in Bath Co. who also married a Hart husband (and if so, Samuel b. 1916 may be their son instead of this couple’s child.)

The reason I say this is that the Kentucky birth index contains a record for John W. Hart, born 1 July 1918 in Bath Co, mother’s maiden name Emma McCarty. This conflicts with the birthdate for Edgar, who is known to be Ellis’s son from his death certificate.

I cannot find any death record for either Samuel or John, nor can I find them in the 1920 census. (There is a John W. Hart son of James Hart and Minnie Blevins, but his birth is recorded on 21 Dec 1918.) So if there was a different Emma McCarty Hart who was the mother of John b. 1918 and possibly Samuel b. 1916, then that couple must have moved out of Kentucky before 1920.

1920 census of Bath Co., Ky, Preston precinct, enumerated 3 Jan, lists on p. 2A as family #25:
Hart, Ellis, 25, farmer; Emma C., wife, 20; Jennie, dau, 10/12. All born Ky Ky Ky.

1930 census of Butler Co., Ohio, Middletown ward 4, enumerated 10 April, lists on p. 15B as family #332/353, at 2213 South Ave.:
Hart, Ellis, 35, age at first marriage 22, cement contractor; Emma, wife, 30, age at first marriage 17; Jennie, dau, 11; Maggie, dau, 7. All born Ky Ky Ky.

The following household is Emma’s parents, Richard and Maggie McCarty.