Thanks Annette and John,
I have previously spotted the Elizabeth Ross that Annette mentions, but have not been convinced that she is the same one.
I have the following on that Elizabeth Ross

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at 1881 census there is an Elizabeth Ross living at 24, High St. Tyrie, age 42, widowed, head of household, born Aberdour, occupation general domestic servant.
In the household are James Cartney age 2 nephew, and Margaret Cartney age 10 daughter both born Tyrie.
Margaret Cartney, illegitimate, is born New Pitsligo on 13th February 1871, mother Elisabeth Cartney or Ross ( shown as widow of Donald Ross, general labourer. IGI has a marriage for this to an elizabeth Curtney 19/11/1859 at New Pitsligo)
James Cartney is born New Pitsligo in 1878.
at 1891 census there is an Elizabeth Ross at 32 High St. New Pitsligo, widow age 52, washerwoman, with William Ross son age 23 mason born Tyrie ( born 13/6/1867 New Pitsligo father Donald Ross mother Elisabeth Cartney ), Elizabeth Webster grandchild age 5 ,scholar b Tyrie, James Ross grandchild age 3, William Mackay, boarder age 1 born Tyrie.
at 1901 census there is an Elizabeth Ross at same address age 62, formerly outdoor working, born new Aberdour, with Elizabeth Ross granddaughter age 14 dom. serv. born New Pitsligo, James White boarder age 4 born New Pitsligo, and James Cartney boarder age 21 mason, born New Pitlsigo.
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If this is her, then at 1881 she is described as widowed, but if so where then is the record of William Lyon's death, and why has she reverted to her maiden name ? Where also is her daughter Mary Ann Mcritchie Ross at 1881 when she would be age 16/17 ?
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On the 1841 census I have found what I believe is the Elizabeth Ross who married William Lyon as follows
Piece: SCT1841/169 Place: Aberdour-Aberdeenshire Enumeration District: 4
Civil Parish: Aberdour Ecclesiastical Parish, Village or Island: -
Folio: 4 Page: 13
Address: Killyquharn
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Surname First name(s) Sex Age Occupation Where Born Remarks
ROSS James M 50 Crofter Aberdeenshire
ROSS Myns F 45 Aberdeenshire ?Forename
ROSS Mary F 14 Aberdeenshire
ROSS James M 7 Aberdeenshire
ROSS Betty F 10m Aberdeenshire
ROSS Anne F 5 Aberdeenshire
MCKAY James M 25 Ag Lab Aberdeenshire
BLAIK Agnes F 22 Female Servant Aberdeenshire
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So you may see why I remain puzzled by this.
I suppose it is possible that they have emigrated, but do not know how to follow that trail.
If anyone has access to the 1871 census then that might throw up a clue or two.
Thanks for your interest and efforts.
puffin