Exponential amplifier thermal stabilisation
It looks like the "stabilisation thermique" circuit is actually a temperature regulator - it dissipates power in the CA3046 to heat it up and servo the IC to a specific temperature! Since the temperature sensor transistor / heater transistor / VCO transistors are all (ideally) thermally coupled, this temperature compensates the VCO core. I've heard this type of technique called an oven controller, and you sometimes see it on test equipment with a high-accuracy frequency reference where the crystal is temperature regulated in a similar manner.

To see why I reached this conclusion, take a look at that thermal circuit. The servo loop inputs are (1) a reference voltage derived from the 12V supply and (2) the Vbe of a transistor. The only feedback path I can see is the thermal one. Now consider what happens to the loop if you magically put it in an initial state where the Vbe of the sensor transistor (connected to pins 6-8) is too high. The op-amp output will rise, the heater BJT (on pins 9-11) will run more current and dissipate more power, the transistor array will heat up, and the Vbe of the NPN 6-8 will go down (Vbe is CTAT).

There are a few limitations to this technique. Obviously, it won't work above some critical ambient temperature. To cover a larger range of ambient temperatures requires higher power dissipation.  The technique also depends on the thermal coupling between the NPNs in the matched array chip. If each of the devices is distributed across the die and interspersed one with another, then thermal matching between e.g. the sensor NPN and the VCO NPNs (not to mention the dTemp introduced between the VCO NPNs themselves!) could be very good.