To my understanding, and I know there are others more well versed that will opine, given your example of engine build date of 0106(Jan.6th), that is irrelevant to the water pump date. You should base it on the cars build date, since this component was added on the assembly line, rather than put on at the engine plant. Assuming the car was built, say,Jan 25th, (for purposes of setting an example), a H2O pump dated anytime prior to Jan 25th would be acceptable. Parts where brought in to the plant in large batches and as used and got down close to the bottom of the batch, a new pallet of parts were introduced and in all probability, a worker took out the few remaining old batch and put them on top to ease accessibility (my own hypothesis). Regardless, it is not unheard to have dates as little as a day up to a few months before build date. I will ad, that at 900+ cars a day, parts were used up quickly and therefore a reasonable date would be within 30 days. This is well covered on the site and many postings if you research this. I would put a link to that information, but will let others, since I am not used to doing such.