The rarity of the appearance of Greco-Bactrian and Indo-Greek kingdoms in ancient literature is one of the reasons why those states are so little-known today. Indo-Greek literature did exist, but none has been found that speaks about the Greco-Bactrian and Indo-Greek states. Classical authors tell us very little about Indo-Greek kingdoms, as they were far away from the Mediterranean world, cut off from other Greeks by the mighty Parthian state. Indian classical literature almost never interested itself in events, except from a religious point of view, and thus does not help to solve the dilemma. Chinese accounts exist, but only supply us with limited information.
This is a companion discussion topic for the original content at https://www.worldhistory.org/article/163/greco-bactrian-and-indo-greek-kingdoms-in-ancient/.