The speckled ones are modern..
I'm holding a bag of them in my hand right now. I bought them at Stater Brothers Market recently. All the marbles in the pic are in the bag. The bag is labeled 'Made in China,assembled in Mexico' and 'Imperial Toy Company,Los Angeles,Ca'. Many if not most foreign-made marbles are copies or near-copies of the old Akro Agate,etc marbles made during the 1930s. This is why it feels so good digging up marbles from old dumps,etc. When you find those you KNOW they're old marbles. I suspect there's a whole lot of ripoff artists out there selling modern marbles to suckers as old marbles.