I have observed the 571 was cased in four different cases during its run.

The first was the "diamonds and bars" unstamped Keystone J.Boss 10K gold filled case. These have been seen encasing 571A movements.

The second was the plain 3055 Keystone J.Boss 10K gold filled case. To date, I have only seen these encasing 571B and 571C movements.

The third was the "diamonds and bars" 3056 stamped Keystone J.Boss 10K gold filled case. To date, these have been observed by myself encasing 571B and 571C movements.

The fourth was the unique stainless steel 3057 Star Watch Case Company case. I have only observed 571C movements in these cases.

With the exception of the 3057 case, the other three cases have the teardrop bow as standard.

The three gold filled cases were only seen in 10K. I have not observed cases otherwise.

Aside from inviting fellow IHC185 members and others to contribute their knowledge in this area, I have a few questions.

Were there any other cases which Elgin encased the 571?

Case popularity: the diamonds and bars cases appear to be the most popular followed by the plain 3055 and the rare 3057 case. I cannot say at present which of the two "diamonds and bars" cases was more popular.

Hypothesized timelines: unstamped "diamonds and bars" cases in 1946 and 1947.
3055 cases from 1948 to end of 571 production.
3056 cases from 1948 to end of 571 production.
3057 cases from 1951 to end of 571 production.

Do these appear to be close to what has been observed by others?

Any other interesting 571 case tidbits?

If I am reinventing the wheel, kindly direct me to previous research/data on this subject. Thank you!

You appear to have missed the 3058 case which is the case that most later 571 type C movements were cased in. This would include the last "I" runs. I would not put to the end on any of the ones that you mentioned, if we take the I serial number prefix as the last range and I 385xxx or I 387xxx as some of the last runs of the 571 those were with a high degree of confidence all 3058 cases.

Wayne's Elgin site shows this

I366001 I366001 22000 BWR 1954 571* 16s o3n20l 21j A5P-A6P j

So I388000 would be the last of the 571's if my math is correct, I have one from I385xxx that is about as new as new can be nearly 60 years after production and I have another one that is even later I387661 which is less than 400 units from the very end and both of these are 3058 cases.

I doubt there are any legit type C 571s in the I serial number range with any case other than 3058.

Here is a 3058 case from the front

back, this watch is like new, there was a sticker on the back with the price that was older than the hills and the rest of the watch looks as good as the back