Honestly, I think you should label only the episodes that really are NSFW, and not just generally. Because if your readers start reading your comic, labelled NSFW, and get used to it NOT having NSFW-content, they might decide it is safe to read at work - and then BAM! Suddenly an episode is full of gore, or nudity, or whatever - and then they're in trouble at work.
Label content that is NSFW, and leave non-NSFW-content unlabelled. That's what the label is there for.
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I am not personally deterred by an NSFW-label as a reader. I work from home - the only one I'll get in trouble with is possibly my cat, and he doesn't really care. I'll read a comic if I find it interesting, regardless of its rating. However, as I am not overly fond of excessive gore, I try to stay away from horror-comics - but that's less to do with how the episodes are labelled, and more to do with my own reading-preferences. I have absolutely no problem with other things that fall under the NSFW-label - nudity, for example.
I haven't had to use the NSFW-label myself yet, as I've kept my levels of violence on more PG-13 levels. However, if I ever were to include NSFW-qualifying content, I'd have to use it. It's only fair to warn people, as some readers WILL be reading this at work, and I don't want them to get in trouble.