logo looks right but heat ring isn't present

[Valentona Hernandez]

I am new to cast iron. Looking to purchase my first piece for cooking in the no. 10 range. It's slightly overwhelming but this site has been a huge help. I have been familiarizing myself with the logo recognition from specific time periods.
I have noticed though, sometimes the logo looks like a particular period but the piece will not have a heat ring when it should or it has a heat ring when it shouldn't. Does that mean that maybe the piece does not fall into the pre-1959 logos?

 

[Doug D.]

The major manufacturers famously did not appear to institute design changes simultaneously across their entire lines. Pattern creation was an expensive proposition, and modifications/updates were often made to existing patterns as time allowed. Griswold can be cited as perhaps the most perplexing in terms of logo changes in combination with smooth bottom or heat ringed pieces. Some makers switched to smooth bottom skillet designs around the 1930s, while others, like Lodge, never abandoned heat rings. Then there are cases where the smaller skillets were seen switched to smooth, but the larger ones were not. If you have a specific example of a piece you are puzzled by and can post a photo or describe the design and markings in detail, we should be able to identify it.