I can't find the correct Shulgin quote to back up the nomenclature right now, but it must have been either in PiHKAL or in Ask Dr. Shulgin. Shulgin declared compounds which first existed as amphetamines and were then brought to their phenethylamines in history of conceiving as 2C-x compounds. Contrary, when the compound first existed as a phenethylamine and then lengthened to an amphetamine, he declared it a 3C-x compound. However, PiHKAL is in its range limited to examples of scaline-derived 3C-x and DOx/ALEPH (DOT-x)-derived 2C-x. But it is clearly stated that 2C stands for 2 carbon (meaning it is a 1-phenyl-2-aminoETHANE), and 3C for 3 carbon (meaning it is a 1-phenyl-2-aminoPROPANE) and by that logic this series would extent to 4C for 4 carbon, yielding the 1-phenyl-2-aminoBUTANEs. Even while historically it has been limited to the scalines (which I'd personally define as anything 3,4,5-trialkoxylated, alkylthioethers being okay too) starting out as phenethylamines, and the DOx starting out as amphetamines, I would not limit it as such. But granted, the whole 2C/3C/4C things, just like the rest of PiHKAL is really messed up. What about 4C-E, for instance. Is it 4-ethoxy-3,5-dimethoxy-a-ethyl-phenethylamine (derived from escaline/3C-E), or 4-ethyl-2,5-dimethoxy-a-ethylphenethylamine (derived from DOEt/2C-E)? In cases like these, we can be grateful that Shulgin was silly and called 2C-D as such and not the more logical 2C-M. But even so
again one could argue that DESOXY (as in 4-desoxymescaline, i.e. 3,5-dimethoxy-4-methylphenethylamine) would deserve to be whimsically shortened to just D (in recognition of the great trivial names mescaline, escaline, isoproscaline, etc. being shortened to their respective initials), and then we would call 3,5-dimethoxy-4-methyl-a-ethylphenethylamine 4C-D too! Isn't that great?
Well, sorry for the rant and all. But it should be clear by now that one shouldn't mix coming first in a chemical space
and tripping frequently at that, like Shulgin did

On the other hand the PiHKAL nomenclature is really interesting because it is a unique case of a quite complex chemical space being attached all kinds of emotions to it. If PiHKAL was just a series of compounds never making it out of academic journals or internal papers within industry, there wouldn't be a need for concise and simple nomenclature. But here we remember the time our ass has been whipped by the 2C-E, the great sex we had on 2C-B, how we had that weird bodyload on TMA-2, how we were enthralled by the visuals on 2C-T-2, etc. So we need those names and often times the needs of a casual user and a chemist are differing. For instance the NBOMe nomenclature is quite interesting because the numbers stand for the position of the methoxys, while the letter stands for the substitutent in position 4. So we could call 2C-B 25B, or we could call mescaline 345, and TMA-1 by extension maybe 3C-345. A lot of derivatives could be named, but then what to do with the FLYs, additional substituents (e.g. 2-bromomescaline, would we call it 345B2?), etc? Well, I like the whimsical nature of PiHKAL nomenclature and the historical implications. I'm often annoyed at people writing "2-CB" instead of 2C-B, but if I'm being honest to myself, if I look through the old pharmacology notebook by Shulgin, these compounds were first actually called 2-Cx compounds. Arguably, 2C-x makes more sense and this is what prevailed.
I agree with my body my rules, but at the same time I'd be happy to see even some of the less polarising derivatives legal and we need to be realistic, change comes slow. I'm not sure what my response would be to give up all the phenethylamines I have known and loved (illegaly) in exchange for 2C-B being legal, but it would give me a long time thinking.