The middle picture shows an open pontil on the base of a cylindrical medicine bottle.
All of the bottle mouths shown below were machine made.
In the 1920s, the bottle mimicked early forms which were hand tooled and sealed with a cork.
The disk-like mark is sometimes confused with a pontil.
the pontil is actually broken glass where the metal rod used to hold the bottle while the lip was form was broken off leaving a sharp scar.
I have put up pictures of the lips so that the readers can see how they mold goes all the way over the top as shown below. This is different than an older hand tooled, hand blown bottle.