I too can only find brief mentions of them. Some points(which might have sidewise relevance) might help

• Kashmir and Its Economy under Hindu Rule (Ancient Period) by M Ahmad (International Journal of Culture and History)
• The book Culture and Political History of Kashmir: Ancient Kashmir by PMK Bamzai might contain relevant stuff
• Gilgit in Ancient times (Tibetology Index)
• Buddhism, diplomacy, and trade: the realignment of Sino-Indian relations, 600-1400

The second one would be the most helpful.

Also,there is the practise of exaggerating in these inscriptions and accounts(like it was said that Devapala of Bengal ruled beyond Kamboja-which is certainly impossible-what is more possible is that maybe a chieftain in that region briefly acknowledged his suzeranity).

Though expeditions to Central Asia from Kashmir are not to be ruled out.

Notes on the Karkotas-their first king was Durlabhavardhana.

And holy shit that map in Wikipedia.Whoever made that map made it without any regard to which regions specifically those tribes and kingdoms mentioned in the Rajatarangini were in that era,and conflating it with modern distributions.It is rubbish,utter rubbish for its Indian parts also. Like at that time(750) Bengal was described as going through a period of matsyanyaya(anarchial chaos) because of a lack of kings,and Gopala,the first Pala ruler was elected to bring an end to this.

And Darda-desa is just the Gilgit-Baltistan region of PoK(The Northern Areas in Pakistani territory).