The serious adverse event definition and rates are defined here: https://health-infobase.canada.ca/covid-19/vaccine-safety/ut...
1 in 9000 doses reportedly results in a SAE, so if you are mandated to take 4 doses, your risk becomes ~0.04% or ~1/2500.
This also does not factor in the risk of "adverse events of special interest", which can be serious or non-serious (though neither seems great for the end user).
And looking at how this page has been updated since the last time I saw it, another red flag is how they separate those out - with a dead link to boot. In my opinion a continuation of efforts that seem intent on obfuscating the ability to make individual risk calculations through this pandemic.
Also more conspiratorially, because I think they would have provided the age-stratified data if it supported their objectives of improving lagging uptake among younger cohorts.
That sounds like motivated bad assumptions.
Seems highly plausible that those who would get the reaction in the 1/9000 would select out the sensitive individuals so the rate would be less for subsequent shots on the other 8999. It seems very unlikely it will be a constant rate.
Anecdotally, I had the same reaction to all four shots. Mild symptoms the lasting 24 hours. With your comment’s assumption that’s pretty statistically unlikely, statistically it would have been likely that one would have been less or more, since by your comments logic it’s completely random.