I'm a native Seattlite (grew up in and call Kirkland home), but I'm studying in Tuebingen for the moment. (Pepper, the ferret, says thanks!)
Thanks for the warm welcome!
I figured that was the case. S'okay to use it in a chat room

but not in a formal essay. No surprise there, but at least " I'd've " didn't having people bouncing up and saying "AHAHAHAHHH! That's horribly wrong!!". Then I'll keep using it

.
I was always told that words that end in 's' took an apostrophe, but no extra 's' -- so sms (plural) should be sms'. I always used 1970's and 100's, because ummmm... that's how I was taught? I wonder if it is because it's you say "in the 1970's" and it's possessive?? Dunno.