Are updates for new functionalities?

You can find here the releases history https://github.com/jsreport/jsreport/releases

What if after 6 months we discovered a bug. Will we be able to receive bug fixes updates after 6 months for a perpetual license?

Unfortunately no, the 6 months are strict to receive updates. Typically enough to develop and stabilize the solution.
However, we typically provide a 25% discount to purchase another 6 months if you get to that need.

How would the pricing work – if we start off with Enterprise Scale One-Time & then, later on, decide to go on to Yearly?

The support can associate your new subscription with the old license key.
We can refund you the original payment if you decide quickly during the 6 months.

How would pricing work – if we start with Enterprise One-time & then later upgrade to Enterprise Scale One-Time?

The support can associate your license with the old license key.
We can refund you the original payment if you decide quickly during the 6 months.