I was thinking that I ought to find a spare key for my 1964 CB77. Figured it was as simple as reading the numbers on the key/ignition T1644 in my case and find a matching key.
I went on ebay and found one for pretty cheap. The shape was slightly different, but the number the same so I bought it. The photo below aren't MY keys but the same kinds of keys.
My current key has the shape on the left, the key I bought has the shape on the right, but they are both stamped TEC T1644. But the one I bought won't work.

I figure:
1. There are either multiple kinds of keys, some of which have the same numerical stamp and you still need the right shape of key aside from that,
2. Or, my key and ignition have worn against each other over the years, and only match one another perfectly, meaning I could never get a spare key hahaha.
Can I get some help on these questions?