In Tyberg's text on p.31 she discusses the transformation of final m.
One example she gives is 'annantyajati' - now she writes it in two
ways:
अन्नन्त्यजति
अन्नंत्यजति
but are they both pronounced the same?
In fact, they can't even be transliterated the same if you use p.2 of
her book as reference.
On p.2 she shows the transliteration of anusvaara was .m or .n ... so
by that alone, there is no way that
'annantyajati' could be written with anusvaara because the only
transliteration she gave for anusvaara was .n or .m
I have a few references on Sanskrit. I don't think Tyberg is giving us
the full picture of anusvaara at all.
In one of my references, a DVD by Saraswati Mohan, she says that the
proper choice for anusvara involves choosing the "n" or "m" sound in
the same class as the consonant.
In Wikner's Sanskrit Introductory, he <
http://groups.google.com/group/
sanskrit-study/web/Wikner%2520Sanskrit%2520Intro.pdf> says there are
true and subsitute anusvaara p.92 of his text. On p.64 he says there
are North and South Indian conventions for choosing anusvaara.
Wikipedia <
http://en.wikipedia.org/wiki/Anusvara#Sanskrit> also has a
rather complex discussion.