Yes 99 is the highest number it will show for anything in inventory. There can be more than 99 items in the stack but will show as 99+.
I run into this a lot when harvesting from the garden.
And I have the same problem with the price of a stack. Like I can harvest my 16 quill fruit plants and I'll keep them in my inventory until the next harvest sense they will increase in price while I carry them. When I first harvest them the stack sells for about $30,000 but when it's time to harvest again I can sell that stack for say $200,000 but if I don't sell them then and I just harvest again the price for the whole stack will drop back down to about $30,000 again even tho I now have twice as many.
