My '70 is turning 39 the 4th week of January (Body plate 01D) and I'm trying to figure out the exact production date. I found the build sheet a while back, but the date block (Block 10) is missing. My car (# 167181) was built at Van Nuys and the last reported VIN by GM for Van Nuys in January was 167285. I'm only 104 units short. I've heard that they built 250 cars a day, so is it safe to estimate it was built the last day of the last month?

The reported dates are not set in stone so to say, because cars outside the range have been found.Another thing to remember, the date on the cowl tag is the week the body was started, not finished. But being that close to the end, you must be very close to the last day of the month, but depending on what day of the week the last day was, it could've ran over into the next month.
Example, if the last weekend of Jan. 1970 was the 30th and the 31st, the car could've had the body started on Jan 29th, and then sent through to the assembly plant on Monday Feb 1st for assembly.
I have seen a build sheet for an Atlanta car marked 1-29, so I do know that cars were built on that day. I'd have to look to see what day that was.

One must remember that cars were assigned sequence numbers before they finally rolled off the end of the line. It took a couple of days at Fisher Body then another day and a half on the final assembly line, assuming everything went according to plan. The date on the build sheet is the scheduled date (and order number) for assembly to begin, not end.

The last VINs reported for any given month at any given plant for any given year must also be taken with a grain of salt. Atlanta (for example) didn't stop the last car assembled at the stroke of midnight on the last working day of the month and note its sequence number so it could be accurately reported. The last reported sequence numbers are more likely the last projected sequence numbers to be built. I have a number of examples of sequence numbers later than those reported for any given month.

Thanks guys, you can't beat TC when it comes to the wealth of knowledge on here.