Hi Michael,
You have absolutely done the right thing getting the cards into sleeves! It's not just dust but also a great way to protect the corners and preserve them for many years to come.
Regarding grading their condition. The following scale is the CSGB guide and the 'Poor/G/VG/Ex/Nr Mint' scale is used by most collectors. Many collectors are very cautious about using the term 'mint' (you'll find sellers on eBay use it all the time though :p):
MINT (Mnt) - The cards must give the appearance of never having been handled, i.e. be in the condition in which they would have come from the printers. Imperfections in the printing process would not affect this (e.g. cards cut slightly off-centre, differences in intensity of ink, marks caused by defective printing plates).
EXCELLENT (Ex) - Cards have been handled but only to a minimum extent and with extreme care, allowing no blemishes.
VERY GOOD (Vg) - Cards completely clean back and front, with no damage. In particular corners would be untouched, but edges might show slight signs of wear.
GOOD (Gd) - Minor blemishes might be visible, due to handling or age, and there could be slight damage to corners. No creases or stains visible.
FAIR (Fr) - Showing signs of considerable handling and consequential corner or edge damage, or a card from one of the above categories with one defect, such as a crack, foxing, dirty mark.
POOR (Pr) - A card that is soiled, damaged or badly worn, or with a serious defect, such as back missing or badly cut down in size.
There is plenty of knowledge on the forum and if you ever want to know anything - just ask!
Thanks,
Sam
