How to check if slot (Slot number) is full?

[retronix]

So im creating a gui basically when you put an item in and press recycle it outputs items into another spot in the gui

https://gyazo.com/19662aa9642a01b571f3bdf9a7a96a9f

When it gets to 64 it just dosent add the rest how do i make it so it will add it to a existing slot?

on rightclick on recycler:
    if data value of clicked block is 0 or 1 or 2 or 3:
        cancel the event
        open virtual chest inventory with size 5 named "&2&lRECYCLER" to player
        loop 45 times:
            format gui slot loop-number -1 of player with gray stained glass named " " to do nothing
        unformat gui slot 19 of player
        unformat gui slot 23 of player
        unformat gui slot 24 of player
        unformat gui slot 25 of player
        if {gui::recycler::current::1} is set:
            set slot 23 of current inventory of player to {gui::recycler::current::1}
        if {gui::recycler::current} is set:
            set slot 19 of current inventory of player to {gui::recycler::current}
        format gui slot 21 of player with anvil:0 named "&a&lClick to Recycle" to run:
            if slot 19 of current inventory of player is iron sword:
                set slot 19 of current inventory of player to air
                add 2 iron ingot to slot 23 of current inventory of player
                add 1 stick to slot 24 of current inventory of player
on inventory close:
    if name of current inventory of player is "&2&lRECYCLER":
        if slot 19 of current inventory of player is not air:
            set {gui::recycler::current} to slot 19 of current inventory of player
        else:
            delete {gui::recycler::current}
        if slot 23 of current inventory of player is not air:
            set {gui::recycler::current::1} to slot 23 of current inventory of player
        else:
            delete {gui::recycler::current::1}