It is you who does not seem to understand that I do understand.
I have already agreed with you that Glenn's TTI allows him to return to 600 regardless of further changes to the timeline. However, his lack of time-traveling afterward means that his existence/memories after this return to the post-Lavos/pre-King Zeal timeline are NOT secured.
This is not Time Bastard. Time Bastard is the removal of alt-timeline versions of time travelers when they reach the age at which their time travel occurred. Marle/Lucca/Robo were erased by regular timeline deletion.
Ah, excuse me. I seem to have misused the term. However, Time Traveler's Immunity is nonetheless of relevance when one starts speaking about "regular timeline deletion"
If, at the beginning of CE, Glenn had traveled from 605 to 1005, met up with Chrono, Lucca and Marle, accompanied them to 2305 and then to -11,995 where the Masamune was taken- The Glenn in CE would be the one who had lived for 5 years in a timeline where the Masamune and Cyrus were still present in history, even though this past was then changed by King Zeal's actions. He would not have lost his memories of this time. After the disappearance of the Masamune, he would then return to a 605 A.D. to find a world in which he, upon his return in 600 A.D. had founded the Vanguard, but would have personally no memory of this, since the Glenn who did that would have become a Time Bastard in 605 A.D. at the point where Glenn left this timeline to meet Chrono, Lucca and Marle in the present.
Since, however, he missed this chance, he loses his Immunity to temporal changes and becomes changed with the timeline.
You know, I'm not sure if this is a good explanation, but it might be better to think of TTI as an event applied to every time travel, not a status granted by time traveling.
Exactly. Glenn was granted TTI at his arrival in 600 AD after the defeat of Lavos, and he would have been granted it again, had he traveled in 605 AD before the actions of King Zeal, as postulated above. As, however, he did not, he was not
immune to said changes, as were Crono, Magus and Glenn himself later on during the Reptite Time-Line Event.
A further interesting question is: What happens when "regular timeline deletion" occurs? Is the person physically the same instance, and is therefore nothing sent to the Darkness Beyond Time? Is it merely a memory-rearrangement executed by the timeline itself? (This would tend to support Bekkler's "Smart Time"-Theory)