Hm.... I don't think that Film Rescue has a secret potion to get results nobody else can get. I guess they simply have a lot of experiance and know f.e. how much restrainer is to be used to prevent excessive fogging and how long to develop to get noticeable blackening etc. They probably know quite good what they are doing. And their statement confirms what also me and a friend experianced.
This friend of mine developed some old, sometimes half exposed films without any whitchcraft, using Rodinal and Promicrol iirc, and got usable results with exposures made 50 years ago or older, but never got a single usable pic from these old films he exposed himself. His darkroom work is very easygoing, more like a noob than a nerd, he's not at all the professor-type of a guy in the darkroom.
I did only one development with a color neg 120 film from the 70s last year. 5 frames were exposed, the rest was unexposed. I unloaded the film in my darkroom and reloaded it into a reliable camera to expose the remaining 7 frames with a guessed exposure index of ISO 25. Assuming that it makes no sense to do a color development I decided to develop for bw in Caffenol-C-L that had proven before to be useful for expired films. I used 1.5 g/l pot. bromide as antifogging agent and semi-stand developed for 70 mins , 20 °C, usually a push 1 - 2 development with fresh film. All 5 old exposures were rather faint but scannable, all 7 recent exposures gave nothing, really nothing at all, completely blank besides the base fog and the brownish color mask. But the 5 old pics with family subjects were rescued.
Your mileage may vary.