This is really late but to add to the previous topic about readopting knuffel...
Yes it works for both retired and current knuffel; I do it a lot with both types.
It just doesn't work for Wild knuffel.
Also, thank you for reminding me about digging!
Oh, and on the leveling up and adopting/readopting knuffel for profit: The maximum point of return in terms of

per xp for that is at level 40.
Level the knuffel to level 40, drop it, readopt it, level it up to 40 again, rinse and repeat.
The amount of time and xp needed per

gained is the lowest when done at that level.
We did the exact math on the forum once, but I don't recall which thread it was in.