Those cans with the pull-up spouts are the same my bro and I bought in the late 50's through 60's. Seems to me, by the 70's when I was buying C&H powder with the same outside can but with screw tops.
I do not recall warnings on the cans fo C&H we bought in the 70's & 80's.
It was not as good a powder as GO (gerheart ownes) or GOEX or even Dupont. On the same 'front/level' as "Meteor" which was made in Scotland.
Perusing Lyman's Black Powder Handbook of the 70's will also show this.