Troffers have been around pretty much since the beginning of fluorescent, but I think the most common style seen today came out in the 1960s or 1970s.

As long as I have been alive, these fixtures are mainstream in commercial lighting. The original ones I think have 4 f40t12 lamps and 2 magnetic rapid start ballasts and has a plastic diffuser with one ballast controlling the outer tubes and another controlling the inner tubes. I have seen these fixtures in 1980s movies and TV shows, but how long have they been around?

looking at an official manufacturing chart I happen to have for the fill gas and pressures of T5 tubes, only the 24W and 39W HO types are Half Neon filled, the 54W 49W and 80W are still Pure Argon, and I think most of the T5 HO tubes you have looked at have been 54W ones?

(although of course there could still be manufacture to manufacture variation)

There are two 54W T5 HO lamps at my floor at my hostel. My father have two 24W T5 HO lamps in his room. Supermarkets here, used to have 49W, 54W or 80W T5 HO lamps.

T5 low current emergency lighting types : Argon + small amount of carbon dioxide

That's interestin. What function does the carbon dioxide has in these lamps?

If there is 40% neon or neon-helium in argon in T5 HO, why I've never seen a red glow discharges at the ends of them?

looking at an official manufacturing chart I happen to have for the fill gas and pressures of T5 tubes, only the 24W and 39W HO types are Half Neon filled, the 54W 49W and 80W are still Pure Argon, and I think most of the T5 HO tubes you have looked at have been 54W ones?

(although of course there could still be manufacture to manufacture variation)

700-series should still be relatively easy to find in all of the typical places, they were super popular. They haven’t been made in over 10 years though, so supply is limited. You should probably be able to find them online pretty easily, though the prices will most likely be astronomical. It might be worth checking your local small hardware store if you have one, my local Ace still has some GE F32T8/SP41s in stock. As for halophosphate, these are super rare. Sylvania made them for a brief time in the early 2010s in response to a triphosphor shortage, but the bans that took place shortly after meant they had to be discontinued. GE also made deluxe halophosphate F32T8s, those were made for an extended period, so they are slightly more common. But all of these F32T8 halophosphate lamps are pretty rare and are probably not something that could be found on demand.

Finished reassembling a vintage fluorescent desk lamp I started restoring last week.

Stumbled upon a house clearing and grabbed a box of random lamps, there's some halogens and incandescents mixed with CFLs and the usual crap LED I'll just resell, if they even work, same with the CFLs, pretty sure they're all 6500K so I won't keep any. It's pretty dusty so I didn't really see what exactly the lamps are yet.

Also grabbed a box fan, 2 floor lamps and an alarm clock, $5 for the bunch, guy wanted $10 but the lamps have broken holders and are overall super loose, and the fan is missing the timer knob. Not sure if the alarm clock even works but there's tape on the cord, so that has to be fixed as well.

Usually because there is mercury vapour present and its discharge colour overpowers that of the gasfilling.  If you place the lamp in a freezer below about -40C and remove the mercury vapour, and ionise the gas filling not too strongly, then you can see the neon discharge colour.

If there is 40% neon or neon-helium in argon in T5 HO, why I've never seen a red glow discharges at the ends of them?