I'm by no means the "expert" on your question, but glad to share what I've gleaned from study of army signal flags, which seem (from the handful of survivors) to have used "sleeves" or ties. (No info on knots, if tied.)

Flags with stitched holes -- grommets -- for attaching may have used leather strips to attach flag to pole.
Flags with attached length of "rope" sewn into the hoist indicative of naval hoisting.
Flags with "sleeves" may have been attached by leather tab inside the sleeve, with tack or screw to receive the tab.
Flags with no ties or other obvious means of attachment may have been literally "tacked" to the pole.

(Army signal fiags presented a special consideration. To avoid wrapping around the pole they needed to be light in weight and free to wave in Myer-Alexander-type visual signaling.)