There was only one study (Taylor (1999)) looking at temporal proximity of vaccination to autism onset.
It NEVER looked at symptom onset rates within 1 week after the shot.
Their study showed it took an average of 19 months before first symptoms until a clinical diagnosis was entered into the medical records.
THE STUDY NEVER TALKED TO ANY OF THE PARENTS, they relied exclusively on what is in the medical records.
So what do parents say if you ask them directly? That 90% of the cases happened within 1 week of a vaccine shot.
But what parents say are considered "anecdotes" by the scientific community and what is in the medical records is considered "science."
This is why there is a huge disconnect between reality and "science."
Autism and measles, mumps, and rubella vaccine: no epidemiological evidence for a causal association , Taylor et al., 1999 in The Lancet.
Key table showing a 19 month gap between the age at regression until it was diagnosed officially:
And then they only looked at 1 and 2 year time frames and relied solely on medical records. They never talked to any parent directly to see if the medical records accurately reflected what happened. This is considered high quality research. Why get your feet wet with a little reality?
But when you have a mean of 19 months from onset to diagnosis, most of the cases will naturally be more than a year from the shot which is what they found as you can see below where 138 cases were diagnosed within 24 months of the shot but only 31 cases within 12 months. It's all because doctors take forever to make a diagnosis, not because onset happen >1 year from the shot.
90% of the parents who recall when it happened, recall that it happened within a week after vaccination.