One of the reasons the 2.50 chips are still in use is they were reordered. The later chips are not brass, but a lighter metal. You can easily detect the difference in chip weight if you heft each in your hand. The reorders are also distinguished by circumferential grooves on the edges, as shown on the bottom chip in the scan.

The cage was collector-friendly and 10 years ago, you could still get unused $2.50's by asking.