Adding the 1722 mixed appearances, there are 3900 appearances in total.
A liquorice shell order can only be satisfied when all three layers have been cleared.
The visible ingredients will drop down to the bottom of the board, then when there is space for them on the conveyor they will drop through the portals and up onto the conveyor.
Level 606 played three times is the best way to get boosters, as pointed out by another poster on an earlier level, but even so I am finding it impossible.
Have a safe trip and a great holiday.
The video below demonstrates how i completed the level.
Good luck to all Rick said.