The best way to tell if you have a Sadler Teapot is to check the stamp on the bottom of the teapot. Every Sadler teapot will say Sadler, and England in some part of the stamp. Pre-1937 stamps say "England J S S B" on the bottom.
I have a sadler tea pot, gold and dark red flowers with green leaves. The stamp on the bottom is embossed with a mark in gold ink either 7441, 9441 or 1441. It has embossed lines around the pot under the flowers.
i have a china teapot, sugar bowl & creamer set wiht the sadler made in England with numbers 1940 mm on them. they have an english country design on the front and back and gold trimming