I just checked in my assortment of bolts. I have 4 old-school hex head VW diesel bolts. 3 of them have no serrations on either bolt or washer. One of them has serrations on both the bottom of the bolt and on the side of the washer that faces the head of the bolt.
To be clear, the bolts I described were specifically old crank sprocket bolts. I didn't state that clearly in my post. My take is that the serrations probably don't matter much.
Doesn't sound like you'd have to chase very far,.. since Libby has some he'll never use he he. If I remember right length of the bolt matters more than serrations on the washer. They didn't always use the washer and the bolt for that crank is a different length.