outdated C-41 developer kits in powder form

Ok - I know, the obvious answer is "just use one and find out", but I'm wondering if anyone would have a baseline idea of how long these kits would keep in powder form - I have two old Jobo C-41 Press kits with all the chemistry in sealed foil packets, but these are more than a couple years past their expiry dates.

My limited lack of experience tells me that if they do not show signs of opening and if they have not been kept in the trunk of a car for those years, they are highly likely to be ok. I have used Unicolor C-41 one liter kits several years after the expiration date without any problems.