I have never paid much attention to it. In fact, I can honestly say I have never know the series of any Panerai I've owned more than a few seconds. I see it on the case back, or somebody may ask, and then I promptly forget about it.
Same goes for SE #s, and yes, T vs L. It either glows a lot for a short period or time, or glows a little for a long period of time.
I just buy em, and wear em because I like the design, and found that the crown protector is a great idea..
WAG MORE Bark Less!