There is an aerial shot that shows the corpses of the garrison hanged by King Stephen, followed by Brother Cadfael's counting them by tens: "seventy... eighty... ninety... five?" In the aerial shot, there are only eighty-five corpses.
In the final credits, the copyright reads MCMXLIV (1944) instead of MCMXCIV (1994).
The caltrops found at 14m30s are made to far too high a standard than would be possible in the 12th century, except for fine metalwork.
There were, in the plot, to be 95 bodies and brother Cadfael also counts 95 bodies but there were only 85 bodies laid out in the courtyard as seen approx. 20 min in. So there were not one corpse too many but nine too few.
For all Season 1 episodes, the copyright year is shown as MCMLXIV (1964) instead of MCMXCIV (1994)
(at around 55 mins) Godith rides away side-saddle. The side-saddle was invented in the 14th century. Before that, women rode pillion (a padded seat behind a male rider) or on a similarly equipped horse behind a servant leading the horse. The side-saddle was created to allow women to ride themselves. (Of course, out of the public view, many women just rode astride no matter what period in history.)