Is it possible the table had a column dropped? Or an update to a previously wide column that made it smaller?

You can duplicate the problem this way:

USE tempdb

GO

IF EXISTS (SELECT * FROM sys.tables WHERE name = 'SizeCheck') DROP TABLE SizeCheck

GO

IF EXISTS (SELECT * FROM sys.tables WHERE name = 'SizeCheck2') DROP TABLE SizeCheck2

GO

CREATE TABLE SizeCheck (

ID INT NOT NULL IDENTITY(1,1) PRIMARY KEY,

Value VARCHAR(8000)

)

INSERT SizeCheck (Value)

SELECT SPACE(8000)

FROM sys.all_objects

UPDATE SizeCheck SET Value = SPACE(1)

SELECT * INTO SizeCheck2 FROM SizeCheck

EXEC sp_spaceused SizeCheck

EXEC sp_spaceused SizeCheck2

/*

name rows reserved data index size unused

SizeCheck1987 16008 KB15896 KB72 KB40 KB

SizeCheck21987 80 KB 48 KB 8 KB24 KB

*/