I went for my nth license conversion test this morning and spoke with a guy from China who actually passed the test in Tokyo but had to retake in Kanagawa. It didn’t make sense to me so I probed further.
Turns out, he registered in Tokyo and failed his first test. And in between, before he passed, he moved to Kanagawa but carried on taking his test in Tokyo. On his third attempt, after he passed, they realised the address on his foreigner card didn’t match the address he had registered with the center and was denied the license. This sounds preposterous to me but serves as a warning to make sure you are staying in the prefecture you are taking the test.
Update: I found out he barely understands Japanese so I’m not certain how accurate the above information is.