"Shipwreck" German handmades make more sense they'd be imported via ship. Can't say the same for machine made marbles, but I'm sure there were plenty left behind at the beach or slingshot for the gulls (oh no)
There was a lot more indigo blue glass at the beach when I was younger, but as a sign of the times it's more green or clear that I see nowadays. Still have a lot since I keep most pieces.