Hey I helped a friend today who has a new Snugride (22#, 29inches) with a base and an old Snugride (20#, 27inches) with a base. Both seats are good(not expired) and both bases are properly installed. If he had just brought the 2 bases I wouldn't have even thought about it... but can the new seat be used in the old base? It fits and locks in... All Graco's website has to say is Snugride must be used with Snugride Base and Safeseat must be used with safeseat base, so it would seem to be ok. I'll send Graco an email also, but I have to get the specific model #'s first.