Candace,
Your original needles do not have a scarf (the indention just above the eye on the backside of the needle). All newer needles do have a scarf. The scarf in the newer needles creates a space so that the zig-zag machine's hook can be set closer to the needle, thereby eliminating skipped stitches. This space in a straight stitch machine effectively places the hook tip slightly farther from the needle and can cause skipped stitches (in a staight stitch machine).
Don't use a non-scarfed needle in an newer zig-zag machine as that can lead to the hook hitting the needle.
Cathy (Just dropping in for a few minutes)