Recently dug up a Rumford 5 Baking Soda Bottle; ie, the number "5" is stamped on the bottom of the bottle. Have seen dozens of identical or very similar bottles on the internet; however, the vast majority of them have no number stamped on the bottom. I did come across a #32, a #7, and reference to a #6. Question is: What is the significance of these numbers? I have found conversations mentioning these numbers, but no discussion about what they mean. Any ideas?