We intuit ex nihilo nihil. Yet if things surreptitiously appeared out of 'thin air', it would be impossible to acertain the so called conservative laws scientifically. This is because both the scenario of creation and manifestation, i.e two totaly different events, would appear as though exactly the same phenomenon to our senses. This also highlight limitation in science (i.e a posteriori knowledge).
This mean we must actualy change how we state the conservative laws of nature. This is to make the scientific statements falsifiable in principle as the 'ex nihilo nihil' isn't discernible from a 'law' that simply forbid manifestations out from the unseen.
Example way of correctly stating a conservative law is to say that the unseen thing cannot turn into the seen at least not without a similar amount of the seen turning into the unseen. As in all cases then, the so called 'laws of nature' look more like 'rules' when close exermined.