As a glassoholic I browse websites, antique shops, auctions, etc. and am constantly amazed (and horrified!) by the amount of incorrect information being pushed out into the world. The internet is a great resource for knowledge, but it's also a way of spreading bad info, wrong info and rubbish very easily.
Some of the myths relating to glass go along the lines of:
If it has a polished pontil mark it musty be Whitefriars. That's just not true, as many makers output has such polished pontil marks.
A ground base dates a piece to the 1930s. This isn't true either, ground bases appear on pieces of all ages!
But the most misleading myth I've seen of late was on a website where it was stated, "The bottom of your new piece of glass will, in nearly every case, offer you some kind of mark or another." Now I don't know the exact statistics, but I do know that this is so far from being true as to merit the status of a glass myth extraordinaire! I have thousands (yes, thousands!) of pieces of glass and a very small percentage of them carry a mark of any kind. I'd estimate less than 10% of my collection is marked in any way. There are makers who claim to mark every piece, and perhaps some do, but I have unmarked examples from some of those who claimed they did, but clearly didn't!
So, if your glass isn't marked, don't be surprised, it's not as uncommon as you might think. There are resources available to help you identify your glass, the Glass Message Board is full of lovely folks who have a wealth of knowledge, and are willing to share it. There are also sites with reference collections of labels and marks - you'll find links to them in my links section in the side panel of the blog.