Pedro,
I believe the reason type XVIIIc were not included is because they are hand-and-a-half swords, and Spenser was only interested in single-handed swords. That being said, I suspect that the reason they weren’t more popular is largely due to the fact that they are so incredibly thin. Skallagrim chipped the edge of his Principe on a branch. That’s modern high carbon steel, and it was damaged that easily. Imagine a similar sword made from inferior steel impacting another hardened steel blade, it would gouge horribly. A second possible reason is that they are seemingly specialized for cloth armor, but steel armor was becoming more prominent during their time. It may simply not have been practical to bring such a specialized weapon into most situations.

Mark,
No worries! I don’t mind being corrected. Only fools despise correction. Besides, that doesn’t seem to be what you were doing. It seems you were more or less expanding what I said for clarity. That being said, I agree with everything you said, I was just giving a Laconian explanation as to why these blades were not more prevalent. I tend not to give details unless they are requested. Since we’re already going down this route, several of the most famous examples of XVIII were found in an arsenal in Alexandria, so it would certainly seem that they were intended for hotter climates wherein you would have been unlikely to encounter any armor that would give pause to using these swords.

Recently I also saw the Skallagrim video about the Principe and was thinking the same thing, I'm really glad it was brought up here.
The extreme thinness as a trade off between ultimate cutting power and durability is a very interesting balance.

Hi guys, thanks for all the thoughts and politeness. And yeah, I agree with it was discussed. And to stop to think about it: do we have any references for medieval people differenciating one blade style from another? So far, all the Portuguese references I came into just treates swords by the use: one handed, longswords, true two handers, falchions (simply called knifes or big knives) etc. They kinda point out they were different from older swords; eg. Fernão Lopes in the 15th century describes swords in the 14th as "mui cortadoras, segundo a usança de seu tempo" (ie. good cutters, according to the usage of their time), indincating swords in the 15th century were proned to thrust, which gave the name of the longswords of the time: estoques

Skal talked about something I don`t know really if it really matters, it's the supposed "agility" that XVIIIc has. I don't own swords, I just handled a lenticular longsword, so, that actually matters?

By the way, I don't know if chronistic evidence should count, but it seems older styles had particularly powerful cutting powers. The Ostrogothic king Odoacer was murdered in a dinner by Theodoric, with a sword blow downwards that opened its way through Odoacer's belly, cutting bones, flesh, and such. Migration Era sword wasn't as balanced as later Viking Age swords were. I think that makes them have a lot of cutting power, and this piece of reference could be proof.

Another source (not that reliable) is from the First Crusade, in a book called "Heroes of the Crusade" that collects lots of sources from the period. After the Conquest of Jerusalem, duke Godfrey de Bouillon was showing his much famed strength among Saracens (some mountain princes visited him because of the stories). He demonstrated that by cutting a camel's head off in a single sword strike. The Sarracens were impressed, one of them even said the sword was enchanted, but he repeated the feat using the Saracen's own sword, Godfrey then concluded that he had such capacity because he never raised his sword against an innocent person. I mean, it might be a legend and such, and when I posted the source in an older thread here, Howard said it was perfectly possible to any sword, but I don't know what you think.

Tuck or estoc just means "long stiff thrusting sword." They can have any style of hilt from a sabre hilt to a longsword.

There are a group of short treatises in Arabic and Persian about different types of sword blade (Khorasani's "Arms and Armour from Iran" has a good summary), and quite a few sources from western Europe in the 14th / 15th / 16th century describe types of sword and dagger for specific purposes. They usually assume you have a basic idea of what a sword or dagger is and add details like "stiff with a point like a grain of barley" or "with a one-and-a-half-edged blade two hands long."

Pedro Paulo Gaião wrote:

Another source (not that reliable) is from the First Crusade, in a book called "Heroes of the Crusade" that collects lots of sources from the period. After the Conquest of Jerusalem, duke Godfrey de Bouillon was showing his much famed strength among Saracens (some mountain princes visited him because of the stories). He demonstrated that by cutting a camel's head off in a single sword strike. The Sarracens were impressed, one of them even said the sword was enchanted, but he repeated the feat using the Saracen's own sword, Godfrey then concluded that he had such capacity because he never raised his sword against an innocent person. I mean, it might be a legend and such, and when I posted the source in an older thread here, Howard said it was perfectly possible to any sword, but I don't know what you think.

I think that comes from Sir Walter Scott's novel "Talisman" published in 1825.