How many are there exactly? I've tried to compile a list of them, and here's what I have so far:

Lucy and Viv Put in a Shower
Lucy's Barbershop Quartet
Lucy and George Burns
Lucy and the Submarine
Lucy, the Bean Queen
Lucy and Paul Winchell
Lucy and the Ring-a-Ding-Ding
Lucy Goes to London
Lucy Gets a Roommate
Lucy and Carol in Palm Springs
Lucy Gets Caught Up in the Draft
Lucy and John Wayne
Lucy and Pat Collins
Lucy and the Monkey
Lucy and Phil Silvers
Lucy's Substitute Secretary
Viv Visits Lucy
Lucy, the Baby Sitter
Main Street, U.S.A.
Lucy Meets the Law
Lucy, the Fight Manager
Lucy and Tennessee Ernie Ford
Lucy Meets Sheldon Leonard
Lucy Meets the Berles
Lucy Gets Trapped
Lucy and the French Movie Star
Lucy, the Starmaker
Lucy Gets Jack Benny's Account
Little Old Lucy
Lucy and Robert Goulet

Are there any others besides these? If so, what sets would they be on?

What I would like to know is, why (and this also goes for other series as well) are there episodes that are "public domain" episodes and episodes that are not public domain episodes?

Was it a way for them to save money back then? If they copyrighted certain episodes, and not others, would that keep them in budget?

What I would like to know is, why (and this also goes for other series as well) are there episodes that are "public domain" episodes and episodes that are not public domain episodes?

Was it a way for them to save money back then? If they copyrighted certain episodes, and not others, would that keep them in budget?

I think that public domain (PD) eps are due to the complicated copyright laws that existed up until the 1980s or so. If I am correct here, each episode had to have its copyright renewed in a small timeframe 28 years after the original copyright, and if they missed this window, then the show fell into PD. 6 eps of "The Dick Van Dyke Show" also fell into PD, as well as 16 eps of "The Andy Griffith Show" and 55(!) B&W eps of "The Beverly Hillbillies". A good number of B&W eps of "Petticoat Junction are also in PD. I have purchased some of these PD eps on DVD since they tend to be cheap. One noticeable difference is the general lack of theme music on these shows, since the theme music falls under a different copyright, so these shows will have either some generic music over the titles, or, as in the case of a set of "The Lucy Show"'s PD eps that I bought on DVD, no credits at all.

What I would like to know is, why (and this also goes for other series as well) are there episodes that are "public domain" episodes and episodes that are not public domain episodes?

Was it a way for them to save money back then? If they copyrighted certain episodes, and not others, would that keep them in budget?

The reason is an employee screw-up. Copyrights expire, and this person failed to have the copyrights renewed on a bunch of episodes of different series.

Speaking of Public Domain episodes, 50 episodes of One Step Beyond wound up in PD and like others, They were issued by Mill Creek Entertainment. I found it and The Lucy Show/Life with Elizabeth set yesterday for $5 each in the Walmart Bargain Bin.

One noticeable difference is the general lack of theme music on these shows, since the theme music falls under a different copyright, so these shows will have either some generic music over the titles, or, as in the case of a set of "The Lucy Show"'s PD eps that I bought on DVD, no credits at all.

For one of my discs of The Lucy Show, that's the case regarding credits. However, I have others released by different companies that include all of the opening and closing credits -- and the Desilu logo at the end. The only thing cut was the name of the sponsor: "Brought to you by...(blank)."

I would love to see fully restored episodes on DVD; the kaliedescope opening is very common, sometimes having been substituted (most likely in syndication -- for uniformity, or just as more modern?) for the original opening with the animated Lucy and Viv that belonged there.