Hi Dave,
It sounds like a special situation, I too import a lot of text files from mainframes and see some very strange things.
I am not certain that I understand the nature of the data. Is it the same each month except for the number and value of cars?
If so, then a storage method that includes in each record a field for the month it came in would allow you to put all the data in one table and extract data for monthly, quarterly, annual, etc. reports.
Are there two different types of records for volume and value?
I do not have a good picture yet of the data or the report you are trying to produce. Perhaps two or three sample records (of each type) with a description of the report you need would help.
alr