Yeah there are a lot less clear cut rules than people realise. Generally anything that comes down to deontological vs utilitarian ethics is heavily debated among vegans. Not eating meat/dairy is super obvious because whether you believe it's morally wrong to kill another living being or are simply looking to reduce the demand so that less animals die overall abstaining from meat makes sense.

But things like wearing a leather jacket you inherited/bought years before being vegan are more complicated. On one hand, wearing an old leather jacket doesn't contribute to the demand/lead to any more deaths but some vegans think it's messed up in the same way that wearing a murder victims skin would be.