Though I certainly haven't seen every Agave out there to see. The Huntington's is not quite as pretty as mine. I'm not bragging--I had nothing to do with it. The plant did the work.
Both have leaves with a slightly scabrous texture.
An Agave expert says A. marmorata, because of the distinctive way the newest leaf emerges encircled by the previous leaf.
The Huntington sign says:
Though of course signs are not to be wholly trusted at botanical gardens, even when they are not very helpful.
Here's my Euro American tissue-cultured A. marmorata, which was for sale a few years ago. EA gave it the common name 'Turtle Teeth' for sales purposes. Heh. It's greener and twice as big as That Agave:
It looked more like the two That Agaves when it was younger:
Not quite the same. Rancho Soledad says of A. marmorata: "This species is variable with some plants being quite large while others...are of more modest size; some have leaves that are a dusky green and sometimes these leaves are distinctly striped in pale blue while others are entirely green or gray."
Here's That Agave's first offset:
Not much of an offsetter. I've gotten one other, and it's small.
Here is That Agave's baby picture, back in 2011. It was a lot more green then than it is now:
Agaves can vary widely within a single species, sometimes so much so as to fool experts for a while. That Agave varies in a good way. It explains why we often see "selections" of a particular plant for sale--the grower liked it better than all the others--it has some particular virtue (cold hardiness, compact growth) or feature (a more eye-catching color) that others of the same species lack.