É possível que eles tenham feito isso.
É possível que eles nunca precisem da Sala Precisa. A única vez que eu posso pensar que eles poderiam ter precisado da Sala Precisa é quando Lupin precisava de um lugar para esconder seu problema de Lobisomem, mas Dumbledore percebeu isso para ele.
"But then Dumbledore became headmaster, and he was sympathetic. He said that as long as we took certain precautions, there was no reason I shouldn't come to school..." Lupin sighed, and looked directly at Harry. "I told you, months ago, that the Whomping Willow was planted the year I came to Hogwarts. The truth is it was planted because I came to Hogwarts. This house" - Lupin looked miserably around the room - "the tunnel that leads to it - they were built for my use. Once a month, I was smuggled out of the castle, into this place, to transform. The tree was placed at the tunnel mouth to stop anyone coming across me while i was dangerous."
- Harry Potter and the Prisoner of Azkaban, Chapter 18 (Moony, Wormtail, Padfoot, And Prongs)
Outra possível explicação é que eles sabiam disso, mas não conseguiam colocá-lo no mapa, porque ele é impossível de ser entarado e a sala tem regras.
The beauty of the Room of Requirement was that it adjusted to nuances. Even the Marauder’s Map couldn’t tell you who was inside it.
- Everything you need to know about the Room of Requirement - Pottermore
Para mim, essa citação significa que, mesmo que os Marotos soubessem, ela era protegida magicamente contra ser colocada no mapa.