plants in nature are crapped on and exposed to the elements. I doubt that any fertiliser for orchids, no matter how old, would damage orchids especially if used weakly weekly. Additionally, not being a chemist, I don't know if chemicals deactivate with age - but presumably you would soon tell if that was the case. The plant wouldn't grow well.
__________________
fine print - anything I say cannot be used against me and ymmv on any growing advice