I did a quick check of my sources to see if I could help with your milk
bottle questions.  I found some information that might be useful in this
book:  Glass Milk Bottles: Their Makers and Marks by Jeffrey L. Giarde,
1980, L.G. Enterprises, Redlands, CA.

Q Milk bottles with S.G.Co. embossed on the heel.
A  Perhaps the Southern Glass Company at Vernon, CA, ca 1917-1931.  My
source does not mention where the mark was placed on milk bottles.

Q S in a Star on milk bottles
A  Perhaps the Southern Glass Company at Vernon, CA, ca 1917-1931.

I found no other info in the book pertinent to your inquiries.

Lee Bennett