Ray Palmer’s Mystic Magazine ran for 16 issues before changing its title to Search Magazine with issue #17. He described the change in Mystic #16 (July 1956):
“So, if horror-comics have sullied the word Mystic, let’s supplant it with one that has distinction, reputation, solidarity, common-sense, and respectability.”
In Search #21, from June 1957, he announced a new title, Flying Saucers, or to be more precise, Flying Saucers from Other Worlds.
He also published a magazine called Other Worlds which I understand was incorporated into Flying Saucers at some point. But in June 1957 the two were separate entities. Here’s the state of things as he described them then:
“We have been completely smothered with mail these past few months, and with Search going monthly, Flying Saucers getting its start, and our science fiction magazine Other Worlds going great guns, we find ourselves the busiest editors in the world!”
“Flying Saucers is a larger magazine than Search being 61/2 x 91/4 inches in size.”
Confounding collectors, Palmer seemed to love changing the titles and sizes of his magazines. Both Other Worlds and Flying Saucers grew larger over their evolutionary runs.