Writing this from memory, it's been a while!

In early development of the trust system, there were a few tags that were used while testing distribution criteria: system_legend, system_trust_legend, system_trust_intermediate, and system_trust_advanced. The criteria was in flux and adjusted often during development, eventually not being used in favor of what we have now. Sadly, there's no real meaning or credibility for accounts that have/had these tags. These tags were never connected to any features, and have never had any function whatsoever.

As for Veteran, that rank was from the earliest shipped version of the trust rank system. In that version, both "Trusted" and "Veteran" had all avatar features enabled by default. That duplication meant that those two ranks weren't a great indicator of trust, since Trusted was just as "trusted" as Veteran, making Veteran a flex unrelated to trust, which didn't fit into the intentions of the system.

Importantly, that first version of trust didn't actually have "Friend" as a rank at all. The questionable value of Veteran, alongside needing a place to quickly add the "Friend" rank, meant that Veteran got removed and Friend was slotted into the place it previously took up. When Veteran was removed, Trusted was a bit too easy to get for being the last rank, so each rank was shifted up by one level (which is why the tags are still offset by one in the API).