The usual practice for many companies is for products with a shelf-life of less than 30 months to have an expiry date, those that will last longer than that will not have one. In some countries this is mandated by law.
It maybe that the product doesn't actually last more than that or it could be that the company hasn't finished testing long enough to determine whether it will last that long yet.
usually it has a 6, 12, 18 or 24 number on the bottom. that's how many months after opening the product you can use it. and they also sometimes put the production date.
I have a paraben free face mask and the production date is 2011 november, I had it for a year now, but it has 6 months on the bottom. Wonder if I should bin that? It still smells the same and hasn't separated, it's a hyaluronic acid mask.