I think RMV was probably thinking of what you did as renewing effective the expiration of your old registration. Your current (through July 2009) registration is still valid, you just lost it.
I'm not sure if inspection will give you a problem. If they raise it you can explain and see what they say. If they run it through the RMV computer you're registered.
What you can do is get a duplicate registration to replace the lost card. You can do it online, in person, by phone, or by mail. They charge $15, though (might be $25 now).
http://www.mass.gov/rmv/regs/reg8.htm
https://secure.rmv.state.ma.us/ITS/T...n/DupForm.aspx