A similar example i founded.

In addition to the missing episode of "The Rose of Versailles". The anime adaption of Sarutobi Ecchan did had 3 supposed episodes mentioned in "The Witch Girl Complete Works" (魔女っ子大全集%20東映動画篇) book but it's never confirmed if they actually existed or made but left unaired or that they were never produced. they were the following

The Tale of Pinocchio (ピノキオ物語)

The Crossing of Tenjin-sama (天神様の踏切)

Ecchan Flys In the Sky (エッちゃん空を飛ぶ)