Yes, umdana. Its been a while. My apologies.
I’m not either sure why the Torah doubles it in other places but not here. I do know that in regards to the sugia of tnai kofel there are exceptions when an umdina is present. I am merely sugesting a route which might lead you to an answer.
Another path to take would be perhaps that the Torah is referring to ??????? ?????????? ??????? as a metzios outcome. Not a scharr.
Bichkosai is clearly a blessing not a direct outcome.
The m’ever hayardain is clearly a promise not a direct outcome.
Any of the cases the gemara brings in regard to the halocha of having tnai kaful between one person and another; chovos, shtaros not direct metzios obviously.
I haven’t looked around and I would not be able to say this on my own but maybe long life is in metzios attributed to kibud av v’em. Respecting ones parents, honouring them, lowering your ego to them can definitely lead to great menuchas hanefesh. Getting a bit too machshavadik now but if there is something there then Rashi is merely stating that the reverse effect is true as well not that it is a promise that the Torah needs to double. Maybe.