. . . And samskr̥ta-, afaik, would be an outrageous violation of articulatory norms and practice in the higher registers of Vedic Sanskrit as well as Epic-Classical Sanskrit.
About 20 years ago I wanted to check to check how vedic priests of the taittiriya sakha pronounced classical sanskrit. I wanted to check this because in their chanting of the taittiriya-samhita, anusvara in certain places is pronounced as a kind of "gum" sound. To do this I collected examples of taittiriya priests chanting the bhagavad-gita. What I found was that in the south (Kerala and Tamil Nadu) taittiriya priests when chanting the bhagavad-gita pronounced anusvara as the class nasal before consonents, but before s ś ṣ y h anusvara was pronounced as "m". This agrees with what Chatterji said about pronunciation of anusvara in the south.
I also checked the pronunciation of anusvara by taittiriya priests from Maharashtra when chanting the bhagavad-gita and there, and the pronounciation of anusvara befroe s ś ṣ y h was similar to what Dominik Haas recommended. I.e. pronouncing an "m" without closing the lips.
Harry Spier