The anime adaptation of Cyborg Kuro-chan was sadly cut short in January 2001 after it's producers (PIBI) became bankrupt and did not have enough money to finish the series. The anime was set to have a total of 78 episodes, 66 of which were aired on TV. It is believed that PIBI began production on episodes 67-71 before their demise. The titles of these episodes do exist which gives us and idea of what they were about.
Episode 67 "謎の雪男現わる!" "nazo no yukiotoko arawaru!" "Mystery of the Abominable Snowman!"
Episode 68 "ライバルはコタロー?" "RAIBARU wa KOTAROU?" "Rival of Kotaro?"
The cover of the script for episode 68 posted to Twitter by Makiko Ohmoto
Episode 69 "キンタローのリベンジ" "KINTAROU no RIBENJI" "Revenge of Kintaro"
Episode 70 コスプレ少女カグヤ KOSUPURE shoujo KAGUYA Cosplay Girl Kaguya
Episode 71 "悪魔になった? 剛くん" "akuma ni natta? Go-kun" "Becoming a Devil? Go-kun"
The promo for episode 69
The promo for episode 70
It is rumored that a preview of episode 67 was played after episode 66 but only in the original broadcast from 6th January 2001 which means that the episode was nearly completed. However the preview only aired in the Kantou region broadcast of the episode which was prepared before knowing that it would be the final episode. Some reference images used by the animators exist for this episode, one of which features two ant like characters who were likely created for this episode
On 23rd January 2016 Japanese voice actress Makiko Ohmoto who provided the voice for the character Matatabi in the Kuro-chan anime posted an image to her Twitter page of a book containing the script of episode 68, she stated that she had never read the script before which suggests that no voice recordings were done for the episode. When Ohmoto was asked if she could reveal anything from the script she replied saying that she couldn't because of copyright issues.
Episodes 67-70 were featured as promos in a Japanese TV magazine known as Telemaga. On 25th December 2014 a Twitter user posted two images showing the magazines that promoted episodes 69 and 70.On these pages we can see the images of the characters Kintaro and Kaguya who were to debut in these unaired episodes, plus in the promo for episode 69 an image of the abominable snowman from episode 67 can be seen. The magazine promos for 67 and 68 don't exist online but were featured in the December 2000 and January 2001 issues of the TV magazine. No images for episode 71 existed meaning that the episode must have been early in production at the time of PIBI going bankrupt.
Since all the episodes of the anime (starting with episode 54) were animated with computers it is likely that everything including the audio and frames were stored on them. It has been over a decade since the anime ended meaning that most if not all the computers used to make it were destroyed or stopped working. It is possible that PIBI gave out some of the storyboards and production sketches when they went bankrupt since they previously did this with some animation cels that were used to make the earlier episodes.
There is some hope for the unaired episodes though. In the recent airing of episode 66 on AT-X a message is displayed at the end of the episode saying "Thank you for watching this anime for a long time. Let's meet again sometime" suggesting that the anime may be continued and there's a possibility that the unaired episodes may get finished or even remade.
A message at the end of episodes 66 "Thank you for watching this anime for a long time. Let's meet again sometime"