In series 1 of Bullseye, the score digits are made up of little white dots.
In series 2, the digits are light blue 7-segment digital ones (i.e. each digit is made up of only horizontal and vertical lines like on an old digital watch.)
Series 3: Same as 2.
Series 4: Same as 2 and 3.
Series 5: Yellow (sometimes white) digits. The round digits are really made up of little straight lines. Zeroes look like flattened hexagons.
Series 6: Blue pixelated digits.
Series 7: Same as 6.
Series 8: Same as 6 and 7, but can also be white.
Series 9: White smooth rounded digits.
Series 10: Same as 9.
Series 11: Same as 9 and 10.
Series 12: Same as 9, 10, 11
Series 13 and 14: Same as 9, 10, 11, 12.
In summary: series 1 had little dots. Series 2, 3, 4 had 7-segment digital numbers. Series 5 had slighty squashed digits made up of straight lines. Series 6, 7, 8 had pixelated digits. Series 9 to 14 had normal digits.
Series 13 and 14 of Bullseye are identical. The opening credits are identical. The sets are identical seemingly to the nearest centimetre. The audience staging is identical. Even the sequence of camera shots is mostly identical. I can see nothing to distinguish them at all, except at the end of the closing credits:
(1) At the very end of Series 14's closing credits before the Central logo, there is a "Carlton UK Productions" solar eclipse logo (it looks like part of a black circle with red fire coming off the edge.)
(2) The date for Series 13 is 1993, but for Series 14, it is 1995.
(3) The Central logo in Series 13 has a plain black background. In Series 14, it has a black velvety (slate?) background like this:
Otherwise, the two series are identical. The placing of everything seems exactly the same. If it weren't for the dates being two years apart, I would say that they were both filmed at the same time, without dismantling the set or putting the cameras away. In fact, I think this might have been the case anyway. I wonder if the production company was superstitious about the number thirteen, or if they promised to make two series and found it easier to film them together.
Note that sometimes an episode from Series 13 or 14 might have the animated Bully's score board closing credits, and sometimes, it might have scrolling text over Jim Bowen talking to the camera. Neither is unique to either series.
As an example of how similar they are, have a look at this collection of pictures from series 13 and 14 showing their similarities.