I would recommend taking all the data from the different sheets and
putting it into one sheet, possibly adding a column for the date or
month. Then you can do all the analysis or summarization you need
easily, using pivot tables or sumproduct or other similar formulas
summarizing into a different sheet. Since you have only about 70 cars
per month, that will amount to only about 840 rows. Even if you have a
row for a car that does not run in a particular month, it still is only
about 1800 rows.

Putting the same type of data in different sheets for different months
can be more trouble than it is worth. If you put the data in the same
sheet, you can still get the effect of seeing only one month at a time
through AutoFilter. Summarization is much simpler with all the results
data on one sheet.

If you woud like to send me a sample spreadsheet I will set it up for
you.

HTH

Declan O'R