If there was only one unmapped city it would be considered rare yet there would still be thousands and thousands of people who could share your anecdote. Adding yours to this thread (albeit without any information about it) brings the number to 2 - for all I know there could be hundreds of them, but there could also only be those 2.

For much of the world no-one has ever done large scale mapping. The Soviet Union and USA produced military mapping and gazetteers for targeting, but it often lacks good on-the-ground knowledge. In rural areas it can be difficult to even get a consistent place name from people who navigate from memory.

Someone in the linked comments talks about adding multiple other cities near this one.

if you can, please add it to osm and add the latlong to Wikipedia!