I have 15 of 8 blades each packages unopened. These are very old, way before the internet became part of my quilting world. Back then all I had for tips and hints were magazines. One article I read said the quilter found useful and cheaper quilting tools at hardware stores and tool supply stores. DH said the only supply store he knew was Harbor Freight. I went there to look around and saw the blades and knew they looked just like the ones in my brand new rotary cutter I was so proud of. They were so cheap, I think .89 a package. I do know the old ones have more metal in them, they weigh more and not paper thin. The newer blades don't sharpen like the old ones either. But you can't beat the price on the blades.
I have so many rotary cutters and I sharpen the blade before I use it so I haven't had to open the packages of blades in all these years. I ran across them not long ago when I was organizing.