The numbers under the feet do indeed act as a "date coder" for the day of manufacture much as with much earlier gens who simply got a year '83 or 2003 stamped.
You will have a 5 digit code...the first number is the year - so 0 = 2010, 1 = 2011 and 2 = 2012...the next 3 numbers are the date of that year so 001 would be 1st of January, 128 would be 7th of May [forgive me if my maths is out there]. The last number will increase the further into the line we go. At the moment, I think all numbers will end with 1 as for HB this is the first manufacturing run of the line. It has also in the past been known to indicate different factory/manufacturer sources. So each factory may have a different number; it depends on the scale of the line but essentially the last number is a HB internal reference and not as relevant as the other dates.
Hope that makes sense
Interesting, I'm going to have to look at the hooves on my G4s now