I joined because I have inherited a TON of kitchen stuff from my grandmother, and my absolute favorite piece is a 10 inch Pyrex Pie Plate

The stamp on my dish is round and looks like the 1950s stamp on the listing here. It reads 229 10 inch and has a K-24 underneath that.
The first issue I keep running into is eBay sellers listing plates as 10 inch when they really read 9.5 inch, then trying to tell me that a 10 inch plate doesn't exist (even though I already own one and am pretty sure I can tell the difference between a 10 and a 9.5)
Second, I've found dished that read 229 and 10 inch, but the K number is different (I've seen K-9 and K-22). I don't know what that means, and don't want to risk buying to plate if it won't be the same size as my existing dish.
Any help guys??! My goal is to own 4 identical pie plates (I bake a lot)