Hi Louis,
The only documentation available for the uploads is the code, I think. (I should make a write-up about the uploads in the FAQ or some other place, now that you mention it..)
Looking at [1], I found that the upload has 3 columns: part number, on-hand and the purchase price. Each uploaded file contains only a single date, if you use this format. If you have a large number of lots to upload, on different days, I would suggest to use the inventory_multi format, which has a leading 'date' column. This column contains the date for the transaction to be created.
The file should always have a single header row which contains the column headers. This row is being ignored.
Regards,
Erik.