Does anyone actually test this code or is most of this stuff just rumors?

According to most of the information I should be able to create multiple variables...

DECLARE @SELECT varchar(100)

DECLARE @FROM varchar(100)

DECLARE @DynamicSQL1 varchar(8000)

DECLARE @DynamicSQL2 varchar(8000)

DECLARE @DynamicSQL3 varchar(8000)

SET @SELECT = 'SELECT '

SET @FROM = 'FROM DATA_SOURCE'

EXEC (@SELECT + @DynamicSQL1 + @DynamicSQL2 + @DynamicSQL3 + @FROM)

The exec statement only accesses the first 8000 characters and then shuts down.

What am I missing/