Puzzle n°43 (*) - The erroneous date

I have two somali breeding females : Aurore d'Alaska (aka "Alaska") and Une Pomponnette, aka "Pompon". Alaska gave birth some time ago. Then, it was Pompon's turn.

I was busy filling the birth declaration for the kittens, which is a mandatory document to be able to later ask for the kittens' pedigrees.
My friend, who was watching me over my shoulder, said :

« Oh, but you made the same mistake again ! You declared a birth date 177 days in advance of the actual one !!!
Do you remember, you did exactly the same error earlier this year when you filled Alaska's litter declaration... »

I had indeed written a wrong date. Probably as a result of my recent anglo-saxon readings, I had written the date in the american format : month/day/year instead of day/month/year ! And this led to a date 177 days in advance. It was exactly the same error again
(and the same cause for it) as for my previous litter.

When were my two litters born ?

... I'm giving up ...