I have a few Mason's myself, but nothing close to your impressive collection. I discovered on the one's I have that every bottle was made by a different glass maker. Which surprises me, and I have no theory or explaination as to why this is the case. I cropped/rotated the photo below because I wasn't sure of the maker's mark. But I see now that it is an "R" in a circle. I have a fairly extensive site of maker's marks, and the following is what came up. None of mine have it! My best "guess" is that the .7 stands for 1947 ???