Not all languages that use a script use all the characters in that script. Some orthographies recognise more vowel sounds than others, so it isn't uncommon for a script to pick up additional symbols as it is adopted by speakers of additional languages. Also, sometimes a script will provide for writing of foreign loan words that include sounds not native to the languages that use the script. However, as you have found, more easily available information about the script in English will tend to favour either the original language of the script or only majority languages, and will tend to favour native use of the script. So, for example, ऑ represents a sound that is not native to Sanskrit or Hindi, but that may occur in English loanwords (I believe the same may be true of ऍ), but this information may not be provided in sources discussing native use of the script.

I've seen them both referred to as 'non-standard letters of the Devanagari script', which is a bit unclear: I think what it means is that they are non-standard in any native orthography of the script, i.e. they are not included in the repertoire of letters in the alphabet. Think of them as being akin to something like ï in English: it is not included in the alphabet and is not a standard inclusion in English orthography, but may be used in the writing of e.g. 'naïve'.

"Jóia" (Jewel) this is a Brazilian (old) slang used when somebody is pleased with something that is given, or explained, to the person in question.

Many thanks.