Was there a shortage of actors??

This was very common in tv at that time. Many, many series recast actors in different parts- this was in the era when shows didn't go into offnetwork syndication until after they had left primetime, no matter how many years they had been on the air (although Ironside actually got syndicated as The Raymond Burr Show in 1974 while in its final season of fresh episodes). Some shows even cast an actor in a guest role or two, liked that actor so juch and then recast them as a series regular or semi-regular.

It could be that some of these actors had a contract with Universal and were put to work in the television series. It's not something that has ever bothered me. In fact, as a viewer I delight in seeing familiar faces in diverse roles.





"It's as red as The Daily Worker and just as sore."

Headblade,
To add to your thoughts about actors appearing in multiple Ironside episodes, add Susan St. James to your list. St. James appeared in two Ironside episodes during Season 1; both of which first aired within TWO MONTHS of each other!
In the first episode "A Girl in the Night" which first aired in Dec. 1967, St. James' character is central to the plot. Assigned to ask her questions concerning her friendship with reputed mob leaders, Ed Brown gets slugged by two thugs. Later, St. James character is found murdered and her death is central to the plot. Two months later in Feb. 1968 Susan St. James re-appears again in the episode "Something for Nothing" in a different character role. This time, she plays the wife of a musician who owes money to the syndicate. Luckily, for her in this second episode, Ms. St. James' character managed to survive without getting killed.
Susan St. James, very young at the time in her early 20's during these two guest appearances on Ironside, was quite an attractive young woman in the late 60's to mid 70's. I can only guess that the director of Ironside must have had a thing for beautiful, early 20's-something women to have her appear twice during that first season. Regarding beautiful women, note first that Barbara Anderson appeared for the first several years as Officer Eve Whitfield, a member of Ironside's handpicked team. Anderson, herself had just turned 22 during the first season of Ironside. When Ms. Anderson left the series in the early 70's, she was followed by Elizabeth Bauer, then in her mid-20's. Ms. Bauer appeared as Officer Fran Belding during the latter years of Ironside's network television run.
I always remember several years later when Susan St. James played the wife of Rock Hudson in the MacMillan and Wife cop show. In the show, there were scenes of St. James shortly before she went to bed with her husband. She always had on that sexy SF 49ers football jersey with her long dark flowing hair, perhaps some panties on, (although the jersey covered them up, as all you saw beneath the jersey were her luscious legs), she was barefoot, and had no other stitch of clothing on. Made me think what a lucky man that MacMillan was, (since he was a much older man compared to his young, gorgeous-looking wife). He got to share a bed romantically, each and every night with a stunning, energetic, and playful young woman. (Of course the irony was that Rock Hudson, as most people know, was a homosexual in real life; being one of the first well-known individuals to die of AIDS back in the mid-80's because of his life style).
But, your theory as to actors appearing in multiple episodes is a valid one.