The Bayesian filter will start blocking emails only after 5000 valid emails and 5000 spam have been received. This is because this filter needs enough initial data on the incoming traffic to make accurate predictions about the future ones. In your case, you only received 1452 good emails, so the Bayesian filter is still in "learning" mode, analyzing the incoming traffic without stopping any.

Also pelase note that, when primed, this filter will be very selective. Most emails will be either 0.001% clean, or 99.99% spam. You will see thus very "clear-cut" probabilities that an email is either spam or not. In addition, since this filter is the one that is applied for last, after all the other filters have been applied, most of the spam will already have been caught by the other filters, so there will be very little left for this filter to stop. Often the Bayesian filter will block less than 0.1% - 1% of the spam when compared to the other filters, as most spam will already have been blocked.

MinEmailsForBayesKickIn=5000

in the SpamFilter.ini file. There's no need to restart SpamFilter after the change.

The Bayesian filter will not log its value in the headers, especially since, as I mentioned earlier, it's only used for less than 1% of the incoming emails, meaning that more than 99% of the email will already have been blocked before the bayesian filter has a chance to look at them, making any stats it would compute for the remaining 1% not very useful.