Maybe you are confussing a missing value ("Not Available") with a character string, in such case you have to test with is.na().
One option is to match empty spaces before and after "no", like \\sno\\s
In regular expressions "." is a metacharacter and means "any character except a newline", if you want to match a literal dot, then you have to scape the metacharacter like this \\.
Also, please consider each new topic as independen from your previous ones, so you have to provide its own sample data and a proper reprex, don't expect people to look for context in your previous posts.