This is from Castrols customer service after I emailed them this
same question...
Our previous Castrol SYNTEC product has been improved, renamed
and repackaged as Castrol EDGE with Syntec Power Technology (SPT)
however it remains in a black bottle and is fully compatible for
use with the previous Castrol SYNTEC product so as always, you can
use the same SAE grade of either product together for 'topping off'
purposes without fear. The new Castrol EDGE with SPT is not only as
good as the previous Castrol SYNTEC product that you were using but
better!