Sure, that can happen. Just not really the case here.
Instances of Blood clots with JJ through December occurred at about the same rate as they were occurring in April, and they all occur within weeks of getting the vaccine.
In April based on the number of blood clots that occurred at the time, you would expect about 32 additional instances of blood clots over their next 8.6 million shots. There were 29 additional instances of blood clots in those next 8.6 million shots.
The risk profile did not really change.