If it still looks and smells normal, it's probably fine. 'best if used by' isn't a hard and fast expiration date. Taste a slice. If it tastes normal, it's fine to eat. Rancid food won't fool you, it'll be nasty!
That being said, I don't use Crisco (or anything else that processed that it lasts for years unrefrigerated) so I don't have personal experience with old Crisco.