We are always faced with the need to make assessments with incomplete information, some of which also inaccurate.
"Predictions are hard, especially about the future" (Yogi Berra)
It is possible that there was a "gotcha" designed into the jab that could be activated at a later date by environmental conditions of some kind. I am certain that multiple researchers considered such things. I am equally certain that they did not have the skills or knowledge or understanding to accomplish such a project. And they still don't.
They just barely managed to engineer a modified coronavirus with some gain-of-function properties which fell apart after a few thousand generations. Then they accidently released it into the wild by sloppy lab procedures, before they knew what it might do.
They are not as smart as they believe themselves to be.
I think of that video where a chimpanzee is given a loaded AK-47 by the guerrilla soldiers. Hilarity ensures.