RELATION: LOT NUMBER - QUALITY OR CLASS - INVENTORY

I'm software engineer, I'm designing a database for registering production process of a sort of product. I'm in doubt about whether to take into consideration the classification of a Product before assing its LOT number or vice versa? Lets say cases a) and b):
a) If PRODUCT-A, for instance, obtains a lot number LOT-1 before classifing it, then that LOT will contain all classes of PRODUCT-A, lets say CLASS-A, B, C, and PRODUCT-A will be included in inventory as only one item, so a further process of classification should divide that production into three parts, one for each class.
b) The other approach is to obtain PRODUCT A, classify it in CLASS-A,B,C, assign lot numbers LOT-1,LOT-2,LOT-3, one for each class and then inventory three lots as three items.

Which one should be the more advisable approach, taking into consideration registration and further quality, or invoicing or any subsequent process ?
Thanks a lot for your comments,
Regards,
Louis.