Alright now let me clean up some points that might have not been addressed clearly. I may repeat some things I have already wrote for the sake of clarity.
1. What I meant when I answered with rabeinu tam about the dam mifkad pakid: It is clear from Rabeinu tam that it is more than just blood that is called dam, being that he says there is two parts one mifkad pakid and yet he calls both of them dam. And they are not the same thing as he says only one of them is used for the dyeing. Also the chavos yair calls this dam and he is clearly talking about the Murex. ??? ?? ????? ?? ??????
2. Coming up once in seventy years, according to the radvaz was a nes that only happened in the chelek of zevulon, explaining why Pliny and others might not bring it down. It is a siman muchachas being that during the time this nes occurred (bizman hamikdash) it only happened to the chilazon. It is interesting to note that this is the only siman of the chilazon the rambam does not bring down.
4. About the time of the when the blood goes bad all that is mevuar from the gemara that as soon as the chilazon dies the blood starts going bad, a point that applies to the Murex. If every extra little bit it is dead the dye is worse, than clearly it is lo niche lei for it to die. And this process of it deteriorating obviously starts from the death and does not start fifteen minutes later, being that there is no chemical change except when it is being killed . So if I were to know from samples every 15 minutes it keeps getting worse, I would then know that it is better when alive and it starts to deteriorate on death. I therefore CAN prove you wrong even from the samples that they have, unlike what you said above.
5. So what about the stira, that according to Rav Yochanan it will appear that you dye it after it is dead and according to Rava it can be done while it is still alive? I quoted a Chasam Sofer (I relized I did not say it bshmo) on this gemara says that it is pashut that they are not arguing on metzious. Rather all Rav Yochanan is saying that you are not oiver for netilas neshama (the gemaras kashya) being that it became a goses during the petzia and therefore is already considered dead. Vayin shum. It would appear, however, that the chasam sofer is arguing with tosafos.
6. Your question from the lashon gufo as opposed to the lashon nartiko, is not even a haarah. We have already discussed that it is definitely a snail. It has a shell ( see ????? ??? ? ??, ??”? ??? ? ??, ?????? ??? ???? ?’ ????, ???? ????? ?’ ?? “?? ???? ?? ?????? ??? ??? ???? ??? ?????? ??? ???”, ??”? ????? (??? ????? ?’, ?????? ????? ??? ????? ?’) ???? ????, ??? ????? ?????”? ?????”? ???? ?’ ?? ?, “?? ???? ????? ?????: ??? ???? ?? ??? ?? ???? ????? ?????”) and you have already decided the gemara will only tell us a siman that helps us identify it. So there is no way gufo does not mean the shell. And if your hanacha is right and it indeed should say nartiko it has nothing to do with the Murex being the chilazon, rather it is a haara on meseches MEnachos 44a.
8. Tosafos does not indicate it is a fish, rather he uses the example of a fish nogea netillas neshama.
Now I think I have addressed all the issues you have raised, and explained why somebody will wear this techeiles. And I still stand by the position I took earlier that I am open to debate whether this is the chilazon or not. But you may say that there are many docheks ( I agree there is a few) involved in assuming the murex is techeiles, This may be true but there is a reason we are so sure of this hanacha. The Yaavetz assumed that techeiles is what the chachmei umos haolam wrote about. The Shiltei giborim (a rishon quoted by the ramban not to be confused with the acharon on the side of the rif) perek 79 “…??? ??? ????? ??????? ???? ????? ??????? ?? ?????”. The ????? ???? in Mekor Chaim 18:2 says: ???????? ????? ??? ????? ??? ???’ ???? ??? ?? ????? ?? ?????? . The Aruch that I quoted above also translates Purpur as the Chilazon.
All this is besides for the fact it fits with most simanim. So even If there is a few not muchach problems there is still raglayim ldavar, and definitely still a safek to which we say safek deoraysah lchumra.