The letter after a part number could be an update (in other words the same
part only updated in some way) or it could be a totally different part for a
newer year car.  It really varies from year to year and from part to part.  I
am sorry this isn't more helpful but maybe if you gave the specific parts you
were wondering about, I could be more helpful.

Thanks,
Ken Wilford
John 3:16
www.vanagain.com
Phone: (856)-765-1583
Fax: (856)-327-2242