Greg Starr would call the 2nd of the first two titanota photos not titanota but a blue oteroi hybrid probably with titanota and mixed in, mainly because the corneous edges are way too developed to fit within the A. titanota variation observed within the A. titanota population at the type locality (Rancho Tambor) - aside from the obvious differences in leaf size and shape. Though the people who collected seed and brought selections like this to market are cagey about about where they did collect, all we know is that it is highly unlikely that they made it to Rancho Tambor - which is the type locality - and which is difficult to get to.
Similarly he would call everything with a midstripe like the one cultivar that PDN brought to market a hybrid as well, in all likelihood with significant kerchovei or oteroi mixed in.
I think GS may be what you'd call an Agave titanota purist, but if you check the actual official description of Agave titanota none of these very toothy cool looking plants actually fit, so maybe he has a point from a taxonomical point of view. On top of that there is a much easier to access population of what is probably best described as agave oteroi merging into a hybrid swarm with kerchovei and some titanota genes. There is kerchovei there, but it is a significant ways away from where titanota occurs. Many of the varieties you see with some kind of titanota label in the trade can be seen growing in the wild there.
There are numerous posts on this subject on Agaveville.org for those willing to dive in...
