Stabilizing allows us to use wood that would otherwise be difficult to turn and finish without large quantities of CA glue to firm it up; but it is not without its problems. Finishing can be one of those problems, and we are often in one of those damned if you do and damned if you don't situations.
Very few, if any, blanks are 100% saturated with the plastic. There will always be some amount of wood fiber exposed on most stabilized blanks. Some blanks are close enough to 100% saturation that it doesn't matter, and it can be treated as a plastic; but most of them aren't. This has nothing to do with who did the stabilizing, it is just the nature of the wood and the stabilization process.
Any exposed wood fiber and the plastic behave differently to finishing, and they wear at different rates. Depending on the wood and the finish, this difference in absorbtion and wear will leave the exposed wood fiber on the finished pen either duller or shinier than the stabilizing plastic. These usually show up as lines in the surface, but they can also be quite large and visible. If the pen was finished as a plastic, and not given a coating of some kind, the wood will almost always wear to a duller gloss than the surrounding plastic. Whether either situation is of any consequence depends on the amount of wood fiber showing through the surface of the plastic, and whether there is enough of it to be seen. The bigger problem is that this difference in wear, and the amount of exposed wood fiber, is something that is often not visible until after the pen has had some wear.
Something we can do is to polish the stabilized pen as though it were a plastic, and then get out the magnifying glass and look for lines of wood fiber in the surface. If there is any doubt about what to do, the safest thing would be to finish the pen as though it were a wood and hope for the best.
Personally, I have had enough problems with finishing stabilized wood that I no longer use it unless there is something that is not available any other way.
