The first set of numbers are a combination of the year code, the plant code and I think also include the month the bag was made, so no, if they don't always match on similar bags it's not a problem. And except for the year code Coach has never disclosed exactly which digits indicate what, but the year code on items made in 2004 or later will always be two digits - 04, 05 etc.
Coach has expanded the serial numbers quite a bit just in the last two years, but for information on earlier numbers, check the Answers to Authenticity Qustions thread, post #34
http://forum.purseblog.com/coach/answers-to-authenticity-questions-94198-3.html