Is to say that something is "never indistinguishable" poor grammar? We rarely, if ever, see such phraseology in English, but my understanding is that it is grammatically valid, even if it would be regarded as "poor grammar"? After all, one could simply say that something is "always distinguishable", which carries the same meaning and sounds much more linguistically valid in the English language. As to why it is poor grammar, it seems to me that this might fall under the category of a double negative? So it would be valid, albeit, considered poor, grammar?
I would appreciate it if people would please take the time to clarify this.