Yes. It's the connection of the prohibited substance with the rider that would be an issue. The connection of a prohibited substance to a support person wouldn't break any WADA code.
Other situations a Team Doctor can order, store and administer prohibited substances within the rules are: Illness, Injury, TUE, Emergency etc.
This is why BC having a store of Triamcinolone went no further with UKAD or WADA because it's not against WADA code to have it in their possession unless connected to an athlete directly. In fact there are numerous legal ways to use Triamcinolone in and out of competition too, so storing it would be expected, it's used for injury all the time and riders are busting up themselves all the time, so treatment would be pretty routine, no differently to that rider going to hospital and having a Triamcinolone injection under provision of the hospital doctor instead to aid their recovery, stop swelling, get back to work again etc.