Christine, that's a good question or two!
And it highlights the fact that there are differences in terminology even with the overall general field of glassmaking.
What follows is my own understanding and I welcome comments by others.
Yes, in a sense, you are correct. The Venetian scramble weight and the Jack Allan surface decorated one could be called "cased" and "uncased". However ...
"Cased" - this is usually (but by no means only) used in connection with hollow vessels, such as vases and bowls. It refers to a covering of clear glass that is not overly thick in comparison to the other layers of the piece. But for paperweights, the norm for a standard domed weight (except for work like the Venetian scrambled weight) is for the clear glass covering to be very thick as this is what provides the magnification effect. And I believe that such a thick coating would not be called a "casing".
But the truth is that I don't know what term is used by various paperweight makers when covering with clear glass. I just think of it as being "another gather" or "an applied coating".
The "after assembly" idea is a good way of thinking about things such as engraving, acid etching etc., but may not be accurate from the designers' or glassmakers' viewpoints. After all, a blank (undecorated) piece is often produced solely for the purpose of final decoration by such as engraving, but it is the engraving etc. that is the real "construction or assembly" (by cutting away the unwanted parts - somewhat like making a sculpture from a chunk of some material) which turns the blank into something special.
For paperweights, my view is that all of the parts of construction / assembly are as important as each other to achieve the required design, but a casing of clear on a vase might only be used to provide a glossy covering to an otherwise unaltered design. For instance, the use of the right amount of clear glass, together with the right form of final shaping, can be crucial in producing the best view of the internal design elements, whether they are millefiori canes, lampwork pieces or an abstract working of colours, bubbles, etc. If the dome of clear glass is not formed correctly, the internal parts will not be displayed properly and if the internal parts are set incorrectly, the error will be enhanced by the dome. This sort of "error enhancemnt" does not normally apply to "cased wares" because the amount of clear glass is not enough to enlarge any defects.