There may be or there may not be. Eurail never announce their sales.

Black friday is something very American and almost non-existent in Europe. Occasionally, there might be an action. If not with interrail, maybe with some of the national operators. But I wouldn't count on it. 

Just check-if it is for a planned trip later on. Also do check 11/11, singles day, not that this is widely celebrated or even known here in EUR-but most passusers tend to be singles.

And yes-as nowhere in EUR here Thanksgiving is done or even known, for us that FRI is very much same-same as any FRI in nov-or oct for that matter.

There also used to be pretty often special sales periods in sept/oct-after main season, nu not this yr-probably they have already doled out all room for discounts with that 50% off on 50th birthday (I took 2, now using the first for 3 months)