It was obviously code 39 but when I made my own version of it using one of the online web barcode generators, the bars didn't look the same. The pattern was very similar but subtly different.
What I discovered is that the intercharacter gap is wide instead of narrow. According to https://en.wikipedia.org/wiki/Code_39, "Characters are separated by an additional narrow space."
I wonder if a larger intercharacter gap made it easier to decode years ago.
So here's the original barcode with a freshly generated version underneath for comparison.
