We have been told that the wishes you grant will be kept on file, so to speak, so that you will be able to make a wish for each wish you grant. However, I have the achievement for 10 wishes granted and have even gone over that, yet it tells me I need to grant a wish to be able to make one? I have definitely not had 10+ of my own wishes granted.
ETA: I have canceled a wish at least once, maybe twice, but certainly not 6 times. Since the Shrub has only been around since the 20th, it's definitely not tracking accurately.
- You can't stockpile wishes like that. If you grant a wish, you're allowed to make one wish. Any additional wishes you grant that same day are "wasted" (for lack of a better word) and won't carry over to the next day.

I wish I was motivated enough to find the post from staff saying that wishes would remain intact for each wish granted, but I definitely remember it.
From here

I am positive there was a staff member who said differently - it was the reason I have been granting ahead and also the reason I made this board. Regardless, it's not a huge concern to me personally and as I said, I'm not wanting to go looking for it, so I give. Happy gifting!
It was on this news post, but only one wish will carry over for you, and only if you didn't actually make a wish the same day.
Thank you for the info! I'm still reading it differently, but I can see it both ways.