In case of the "missing" letter (called khanda-ta in Bengali) for the Bengali equivalent of "suddenly", historically, it has been a derivative of the ta-halant form (ত + ্ + ). As the language evolved, khanda-ta became a grapheme of its own, and Unicode 4.1 did encode it as a distinct grapheme. A nicely written review of the discussions around the addition can be found here: http://www.unicode.org/L2/L2004/04252-khanda-ta-review.pdf
I could write the author's name fine: আদিত্য. A search with the string in the Bengali version of Wikipedia pulls up quite a few results as well, so other people are writing it too. The final "letter" in that string is a compound character, and there's no clear evidence that it needs to be treated as an independent one. Even while in primary school, we were taught the final "letter" in the author's name as a conjunct. In contrast, for the khanda-ta case, it could be shown that modern Bengali dictionaries explicitly referred to khanda-ta as an independent character.
For me, many of these problems are more of an input issue, than an encoding issue. Non latin languages have had to shoe-horn their script onto keyboard layouts designed for latin-scripts, and that has been always suboptimal. With touch devices we have newer ways to think about this problem, and people are starting to try out things.
[Disclosure: I was involved in the Unicode discussions about khanda-ta (I was not affiliated with a consortium member) and I have been involved with Indic localization projects for the past 15 years]