Totally agree with Big Rob on this one. As long as you're you're not breaking an ADR you'd run out your old stock before your ordered new in.
A couple years back the company I work for changed the housing colours of our products, however I'm still occasionally installing parts from stock in the old housing. On books somewhere it would say that from date X we used the new colour, but there is no way we'd bin good parts for a colour change, or in the case no way they'd bin the old nuts because they decided to get a cheaper to make nut.