@LightBulbFun did you ever happen to compile a list of these oddball tubes?

Commutating ferrite ring will saturate more quickly when load current increases...

The ring saturates, but because the frequency and mainly the current slope gets higher and amplitude increase the base drive (the voltage across the ring gets way higher, increasing the base drive way beyond what the transistor needs for the currents, so causes the Ts to go way higher), the quite long storage time in the transistors makes the current to go way larger. And this effect causes the current to go way beyond the normal operating current.
It is not uncommon to see currents 3x higher than normal, but more like 5x...
In reality the opposite is more of a problem: To keep the current from soaring really high, saturating the main inductor and frying the transistors, mainly when the lamp ignition fails (normally the high current rise is stopped by the discharge clamping the voltage across the resonant capacitor).

Also without this much of current boost, it won't be able to generate sufficient voltage for discharge ignition.
Taking an example with a 11W, 0.15A lamp, series inductor about 3mH, resonant capacitor 2.2nF, neglect the series coupling capacitor for the simplicity (it makes the things even worse, as it efectively reduces the inductance), fed from rectified 230V so about 300VDC so about 150VAC at the halfbridge.
Normal operating frequency would be about 36..40kHz, yielding the 0.15Arms (L/R time constant fed by a square wave).
A starting frequency around 140kHz would yield about 0.45A and barely 220Vrms across the capacitor (Vstart = Ires * (1/(2*Pi*Freq); 150V/Ires = 2*Pi*Freq*L - 1/(2*Pi*Freq*C); assume operating on the inductive resonance side). And that is already quite low, even when speaking about 140kHz.
The 140kHz means 3.5us long pulses, only the second half of it is carried by the transistor itself (the first comes from the parallel diode, because it flows in the opposite direction) so about 1.75us while the Ts of the transistors use to be in the 1.5us ballpark. So the ring core saturation needs to happen about 250ns after the current zero cross, which corresponds to about 0.15A saturation current it would have for normal operation.

Check out the Chamber of Commerce and the Trademark Bureau websites/archives of the country where that company is from.

The Chamber of Commerce has information on whether a company still formally exists or not, the address where it's registered (which may help you find more info) etc. If it doesn't, the Trademark Bureau can point you in the direction of the new trademark owners, which in turn may be the owners of the intellectual property (like lamp designs, formulas and such). Or if the trademark is lapsed, it's likely that it's all gone or just in the private ownership of one of the former company owners.

So I won't be surprised to see 0.12A lamp with filaments requiring 0.5A for preheating (while standard T5 are designed for ~0.16A discharge and ~0.24A preheat currents).

It will not be possible to achieve in a simple 2-transistor series resonant circuit typically used for such tubes. Such inverter displays inherent current-limiting behavior by itself. Commutating ferrite ring will saturate more quickly when load current increases, increasing inverter frequency and so backing off the current. So preheat current may be in range or just slightly above nominal tube current.

One can do it with a more complicated circuit typically used in non-integrated HF ballasts, involving auxiliary windings on the ballast choke.

Well said!

Yeah, heaps of companies just silently ceased operations, perhaps @LightsoftheWest will know?

Quite possibly. It is rather annoying that we are in the age of information yet some information regarding things that have happened recently is hard to find.

Yeah, heaps of companies just silently ceased operations, perhaps @LightsoftheWest will know?

I'm sorry to hear that, that sounds like classic postal services, breaking/loosing stuff and not taking responsibility.

You may have seen a picture of a QL Design 114-24B in my gallery. If not, see it here: https://www.lighting-gallery.net/gallery/displayimage.php?album=8815&pos=32&pid=255280
After some searches on the topic, I could not find any relevant information on what happened to the brand, despite countless brochures for their various fixtures being available on Scribd. So, what happened to the brand?

Unfortunately, the tubes never made it here so I’ve put this project on the back burner for a while. I’ll try to find some other cool vintage tubes to use for the DIY light fixture, but right now I sort of lost motivation when the tubes didn’t make it. The postal service managed to screw up really bad and somehow they got stopped at one of their terminals and sent to a wrong address and it just became a huge mess. I don’t even know if the seller got them returned, I doubt it because I haven’t got a refund I’m very much at a loss and I don’t know what to do to correct this, the postal service is not being helpful whatsoever in resolving the lost package.