Hm. Looking at the Foal in a can factory, Foalcan production guide and the original appearance of Avocado it is true that excess waste was squeezed out of the foal and a waste plug was inserted. However, I don’t know if this indicated that the foal was actually “corked” per se - it could be a means of further cleaning out excess fecal matter from the foal. Also, the can was described as smelly at the time Avocado came out, though that could be from the urine and not necessarily fecal matter.
I guess it would help if @Carpdime can confirm foalcans were supposed to be corked or not.