@shiva linga

You know so much, it's great to have a proper discussion and sharing-learning of information.

Yes, Malla was a title then. The later Mallas of Kathmandu Valley are all descended from Hari Simha Dev who was Karnat dynasty king of Mithila. The history of Karnat kings goes from Mithila to Delhi to Konkan to Ayodhya (Ram's birthplace) and Mallas themselves stylised themselves as Raghuvamshi (there still is a surname among the Chatharis with this surname which means Raghu's dynasty.) Also note that Konkan is in South India where the Gopal-rajvamshawali states that Hari Simha Deva did indeed come along with few specific castes like Brahmin (today's Rajopadhyaya), Vaidya, Bhandari (today's Rajbhandari), Rathaur (today's Gongal, Piya, certain other Bhaktapure Chatharis ) and among others the warrior Nayar caste. If you do not know already, google Newar and Nayar similarity. Some believe Nayar turned into 'Naya' - the Newari word for the butcher caste consisting of Khadgis, Shahis of today. The Malla kings adopted the title of Malla as a continuation of the previous dynasty (pre 14th century) who called themselves as Malla because Malla title belonged to a prestigious 'mahajanpad' ruling Vedic clans; those Mallas ruled around Mithila/Bihar in the earlier period under Maurya - Gupta empires. So it was basically a matter of prestige to adopt the word. The Khas Mallas of the Karnali valley did exactly the same thing precisely because of the same reason. However, the Khas Mallas and Nepalmandal (Newar) Mallas were/are of different backgrounds. Newar Mallas were Maithili-speakers with Maithili background and had a bigger amount of 'Indian' blood since they mostly married into princes and princesses brought from present Indian states. They and their ruling Hindu Chathari/Kshatri clans that immigrated to Nepal are the biggest influencers of 'Sanskritization'/Brahminical hold of the already existing indigenous Newars. Khas Mallas were Pahari-Khasbhasa speakers with distinct intermixture with Mongoloid influences of Tibetan and Magar blood. This also shows that what we call the present day Khas-Thakuri people have a good chunk of Magar heritage/origin.

And regarding the surnames, I have seen plenty of specifically Shahi, Singh, Malla, who specifically write Shahi-Thakuri, Malla-Thakuri etc. most probably to avoid being taken as Newar Shahi/Singh/Malla. But you don't find Newar Mallas writng Malla-Thakur or even Malla-Newar. Dasarath Chand the great martyr used to write Dasarath Chand Thakur. But writing -Thakuri as their surnames seems to be a pretty recent phenomenon I suppose. Older generation Khas Thakuris I know didn't write such. Among the names you mentioned, the cricketer Gyanendra Malla is a Newar Thakuri not Khas Thakuri.