Corrected entry: The episode "Bells" and the episode "Head" appear to be inversed in their order - Lord Percy has a beard at the beginning of "Bells," and shaves it off. However, in "Head," he's got it back. In all of the other episodes, he has no beard. Also, the song at the end of "Head" mentions Lord Blackadder's origins (it mentions Edmund's great-grandfather), which makes it more a follow-on from the 1st series.
Corrected entry: Blackadder's house is confusing, particularly the "front" room we spend the series in. In "Potato", Blackadder fires an arrow down on the crowd, and calls down, showing that that room is on the second floor. In "Beer", this room leads into the corridor (which is level with the room), and the front door is level with the street, as shown by the Puritans entering.
Correction: The street that the front door opens out onto need not be at the same level as the street outside the window. The house could be built on the side of a hill so the streets might not be at the same height.
Correction: Very much your opinion though. The episodes do not necessarily follow directly on from one another (remember, due to the later episode Potato, the beginning and end of the series are separated by several years), giving a fashion follower like Lord Percy plenty of time to grow a beard and shave it off again. These episodes have not been re-ordered on the subsequent DVD releases, or in the book 'Blackadder: The Whole Damn Dynasty' (written by the show's writers Richard Curtis, Ben Elton and John Lloyd), as they surely would have had it been a broadcast error. It must therefore be assumed to be intentional on the part of the makers and not a mistake. Equally, the song only mentions Edmund's ancestor because it fits vaguely in with the idea of Blackadder achieving a little bit of power again, and would have fitted anywhere in the series.
umathegreatstationarybear