Frankly, I would think you'd understand that facts from the 1860's are really the best measure of the smallpox vaccine's success since that is when the majority of the world's epidemics took place and since it is also the largest body of recorded evidence available to us. Since there is hard data for the time period and since that time there have been relatively few epidemics, it's quite appropriate to rely on it.
There are quite a few very good and honest researchers who point out that not only are diseases such as smallpox, bubonic plague (for which there is no vaccine) and polio demonstrably cyclical in nature and there are other factors which may be more significant in the disappearance of the disease, it cannot be said with any measure of confidence that any of them have been erradicated.
Most certainly not due to vaccinations.
As has been pointed out, the improvement of sanitation has more affect on mortality rates and infection rates than anything including vaccines. And there is a mountain of data to suggest that vaccines in fact have the oppposite affect on infection and mortality rates.
Polio for instance was known to be (and still is for that matter) tranmitted through human waste (FDR contracted his case by swimming in a creek contaminated with human sewage).
The 1950's in America was a time when many communities were developing waste treatment facilities.
When the Polio vaccine still contained the live virus, it was recommended that anyone not vaccinated refrain from coming into contact with the infant recently vaccinated since the most likely source of infection would come from his soiled diapers. Even without the live virus, that has been the identified source of many reported polio cases in the US. In fact since 1970 there has not been a single case of polio not associated with the vaccine. Zero. Nada.
And given what we know (what some small number of us anyway) about the disasterous affects of vaccination campaigns during the above time period coupled with the fact that WHO and CDC have discontinued vaccinations because they feel they are no longer necessary, you have the ripe situation for a new disaster when the next epidemic is "treated" once again with mass, compulsive vaccinations foisted on the millions of people never vaccinated but propagandized into believing that the vaccine will protect them.