Pilots are routine for television production especially comedies. Ricky Gervais and Stephen Merchant used their own money to make the pilot for The Office.
It allows the production company to to analyse what works, what does not, what kinks need ironing out before vast sums of money is spent on whole production being greelit.
Sometimes the script is not fully polished, set and costumes are not fully realised.
The shock with the Blackadder pilot was how faithful it was to the second series onwards when Ben Elton was drafted in as co-writer with Richard Curtis.
The first series of Blackadder had Rowan Atkinson as co-writer. It was an expensive series as it had a lot of outside location shooting and expensive guest stars such as Peter Cook.
It was also uneven with its comedy, Blackadder was a simpering idiot. In the pilot he is more cunning and conniving although his plan which comes to fruition was originally an idea formulated by Baldrick. However another actor plays the manservant Baldrick.
The basis of the plot was used in the second episode of Blackadder. Edmund's Scottish lands are given to the heroic warrior, Douglas McAngus. He is played by Alex Norton in the pilot as well as the series.
The pilot was very good as a work in progress. It lacked polish here or there but they got the persona of Blackadder spot on. So it was surprising when it went to a full series production, the main character of Blackadder was altered so much.
It was also a shock to see Robert Bathurst playing Blackadder's older brother in one of his first main roles. He too was later replaced.