Did it come about through an incorrect transcription or a formal change.

David,
as the earlier replies suggest, I doubt either of the above theories apply, especially the latter. I suggest it's all down to the "lack" of perceived literacy skills which affected most forms of written text up until the late Victorian times when national schooling became the norm, where people wrote what they'd heard, or thought they'd heard, not helped by strong Forest dialects of course.

Looking at the fairly recent Trade Directories in the following list shows the publishers were themselves unsure (much as on the Ordnance Survey maps of the time), but many give history references which if anything suggest maybe it should be spelt with double "b"s haha. Often the "educated" scribes and authors who wrote these histories or produced the maps etc would spell things how they thought they should be spelt using the convention of their own time or education, sometimes with a disregard for what might be the true spelling !

http://freepages.rootsweb.com/~cbennett/genealogy/index.htm

Abinghall

1750-1799 4

1800-1849 220

1850-1899 704

1900-1949 170

1950-1999 1

Abenhall

1750-1799 0

1800-1849 13

1850-1899 282

1900-1949 987

1950-1999 17

It’s not a perfect way of looking at it since coverage in the earliest and latest years is rather sparser than in the 19th and early 20th centuries. However, it does seem to show that both names were in use over a long period but that Abenhall gradually displaced Abinghall as the favoured form, at least in print.

1596 onwards ) Abenhall is hand-written

1762 onwards Abbenhall is hand-written

1804 onwards Abinghall

Searching the National Archives -

John de ABBENHALL (ABINGHALL) Gloucester dated 8 July 1316 to 7 July 1317

? Not sure who he is

also

Dated 1200 held at Gloucestershire Archives

Gift for 10 shillings (i) Sir Ralph de Abehale

Dean of Mitcheldean. Gift for 10 shillings (i) Sir Ralph de Abenhall etc one piece of land in town of Dene (Mitcheldean)

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Checking with the Gloucestershire Records Office for Wills - the earlier ones list Abenhall - and around early 1800 Abinghall.

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Various websites

Reginald de Abenhall, Knight died 1341

The "de Abenhall" family, while originally from Abenhall, were tenants of a moiety of the manor of Dene. etc etc.

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Old maps on this website

Glocester to Monmouth 1720 - written as Aben Hall

Gloucestershire West 1787 - Abenhall