Since updating to 1.12, you cannot use /give or /replaceitem to give yourself more than one unstackable item at any single time, or more items than the maximum amount stackable. In 1.11.x, this was not the case, as you could give yourself up to 64 of any item, even if the item is unstackable or has a limit to the amount stackable.

This is the command output that you receive when you attempt to give yourself more than one unstackable item at any single time, x representing how many items to give.

[13:22:58] The number you have entered (x) is too big, it must be at most 1