according to your standard,they don't always become erect, some are semi. What were the parents ears like?
For gsd who have free standing ears,(meaning no surgery is required, and is a fault if surgery is done to their ears) I tell new parents to leave the ears alone, don't even pet them backwards, (from eye to back of head) dont' rub them at all, it breaks down the cartilidge in there. They should stand on their own if they are going to do so, before 4 months old, (unless they have larger than normal ears), if they aren't up by then, the teeth take all calcium for production of themselves, until around 6-7 months old, then the ears can get more, and they should stand within a few months.
Some ppl cheat and use a spongy roller used on hair, and some eyelash glue, and put the roller inside the ear in the pink area of flesh, to help stand, if they have to do that I tell them not to breed the dog, and those that have to surgicaly fix it, are disqualified from show, and it isn't very pleasant for the dog either.