Injection marks bruise?

Charley

So my partner is a recovering heroin addict. He used to inject or smoke it, you could mostly tell when he injected as his arm join would be red and raised. But as far as I know and as far as he is telling me his last use was the 31st January 2020, but recently his arm where you would inject looks bruised, I don't think I noticed before and I am sure I would have. Would injection sites still appear to be bruised with 5 and a half months of no use?