"deemed as"? "based on" vs. "based off of"?

A Facebook friend who was grading papers wrote:

Fellow language/grammar enthusiasts: I need another verdict so I know if two more of my pet peeves are justified. My students write that something is "deemed as" rather than simply "deemed" the adjective that follows. They also write that things are "based off of" rather than "based on" other things. I hate both. May I correct them or are these now so common as to be legitimate?

I responded:

This is the kind of thing I love to go a little bit crazy with …

I looked up the phrases in the Corpus of Contemporary American English (COCA) and the Corpus of Global Web-Based English (GLOWBE). These two corpora can be found at the BYU site for linguistic corpora.

For based on vs. based off of:

COCA
based on = 61860
based off of = 9

GLOWBE
based on = 335832 (US 76525)
based off of = 736 (US 392)

I think you can safely say that “based off of” is not yet Standard English.

Deemed (as): this pair is a bit harder to deal with, because it’s not two distinct phrases (i.e., all hits for “deemed” as are also counted for “deemed”, and many of the uses of “deemed” might be in contexts where “deemed as” would not be used). But here are the numbers:

COCA
deemed as = 56
deemed (including the above) = 5141

GLOWBE
deemed as = 1419 (US 136)
deemed (including the above) = 39523 (US 5512)

While these ratios lean quite strongly in favor of not using “as” with “deemed,” I think there’s enough uncertainty about the numbers to make “deemed as” worth accepting, as well as enough grounds for understanding where “deemed as” comes from (parallel to “regard as” and “consider as” — which latter form I don’t like, actually, but have to admit exists).

This is only about current usage (1990-2012 with COCA, 2012-2013 with Glowbe), so it doesn’t even address the history of “deemed as” and “based off of.” I bet the former has a long history, while the latter doesn’t. But linguists have a term to refer to people’s sense that a construction is new when it is not: “recency illusion”.

And the Google Books Corpus shows that I’m right: “base d off of” does not appear until the 1990s in American English (though it has risen sharply since). In contrast, “deemed as” has been in steady use for 200 years now.

So mark “based off of” as wrong (and discuss it?), but accept “deemed as” (and talk about the “recency illusion”?).