Irregardless is a word.[74][75] Nonstandard, slang, or colloquial terms used by English speakers are sometimes alleged not to be real words, despite appearing in numerous dictionaries. All words in English became accepted by being commonly used for a certain period of time; thus, there are many vernacular words currently not accepted as part of the standard language, or regarded as inappropriate in formal speech or writing, but the idea that they are not words is a misconception.[76] Other examples of words that are sometimes alleged not to be words include burglarize, licit,[77] and funnest[78] which appear in numerous dictionaries as English words.[79]

https://en.m.wikipedia.org/wiki/List_of_common_misconception...

This specific case has been addressed multiple times by an authority. https://www.merriam-webster.com/words-at-play/could-couldnt-...