In the Paramount Widescreen Collection edition during the lottery scene the man drawing the tiles reads the name "Princess Elspeth Ophelus; Filia Regis". Filia Regis is Latin for "Daughter of the King". The subtitles read differently, instead of Filia Regis it reads "Clearly outrageous".
The final battle with the dragon takes place during an eclipse and a magically-summoned thunderstorm. However, when the dragon rises above the cloud cover for its final attack, it's in full sunlight.
"Twice each year, at the Spring and Summer Equinox, the king selects a new victim." The seasons are: Spring-Equinox (Day and Night of equal length); Summer-Solstice (longest day, shortest night); Autumn-Equinox; Winter-Solstice (Shortest day, longest night). There is no Summer equinox.
In the film a solar eclipse takes place. This happens by the moon sliding in front of the sun, from below. In reality the moon moves from right to left (northern hemisphere) or left to right (southern hemisphere).
Obvious matte work during some of the flying sequences and when the dragon is moving on the ground.
When the first girl is chained up for the dragon. She wrenches her hand free from the shackles. Then you can clearly see the soft padding inside the shackles for a couple of shots. Later when the shackles are shown in the film. There they have been switched to plain metal.
In the dragon's lair, a wizard sees in the water in front of him the reflection of a dragon as it rises up behind him. Reflections would only reveal things in front of or the above a person looking at a flat surface such as water. He might hear the water dripping from the dragon, but seeing the dragon's reflection in the water is impossible.
During the scene in which the wizard teleports himself to the mountaintop for the final battle, thunder continually rumbles under a clear sky in the soundtrack even though the wizard hasn't yet magically summoned the electrical storm (which he will do in a few moments).