I believe "I came upon my medal yesterday" should be accepted and have reported it.
There are two different bonn words, identical in gender and declensions; “tyre” is among the meanings of the first bonn, and “medal” is among the meanings of the second bonn.
(In the old orthography, the first bonn had a plural declension of bonnaidhe, and the second bonn had a plural declension of buinn. Now they both have boinn as their plural.)
I came upon my medal, I happened on my medal, I came on my medal, I found my medal, - idiomatically it all means I found my medal
What does this sentence mean exactly? When would it be used? It seems like a strange thing to say, unless is means idiomatically "I won my medal yesterday"?
It means “I accidentally encountered my medal yesterday”, e.g. while in the process of trying to find something else, I found my medal.
If you just announced this without any other introduction you wouldn't know whether you meant a tire, a coin, a medal.