What they mean to say is "we couldn't be arsed to keep accurate information posted about our varying stock of mostly-interchangeable products, because maybe one in a hundred customers actually cares enough to weigh these things" so congratulations on being in the upper 1% !!
Like
@Poppin92 said, any particular product from any particular factory is going to be very consistent. But different factories will manufacture different products which might
resemble each other but be different in certain details, such as weight. Distributors will source their products from various factories, and retailers will source their inventory from various distributors. So a retailer might list "super diamonds" on their website, but when they sell out of their inventory and want to restock they might order a different product from a different distributor that's
similar and so will also list it as "super diamonds" and just not bother to update the listing to note that the weight is different. They might also be thinner or thicker or be made from a different materials or have different colors or (even worse) different shades of the same colors.
The less generic a product is, the more likely it is to be consistent between retailers and across time, because a uniquely-branded product is more likely to be sourced from a single supplier. For example, probably all the Milanos you're going to come across, no matter who you get them from or when you get them, are going to be as close to identical as is reasonable (there will still be some variations, especially in color, because dye lots vary over time and it's very difficult, or rather very expensive, for manufacturers to make them perfectly consistent). But super diamonds are generic; they're made and sold by lots of different people.
