Using an existing Canasta to pick up the discard pile

Question

I understand that you can pick up the top discard (and then the whole discard pile) if the pile is not frozen, and the top card matches a meld you have on the table.

I have some friends who play that you cannot do this if the meld is already a canasta. That makes a matching card a much safer discard - the opponent could conceivably still take the pile with matching cards from their hand, but if they already have a canasta of the same cards on the table, this is much less likely.

Any opinions, or definitive rules on this?

Answer 1

Yes, you can add to a Canasta just like you can add to any other meld.

Source:

Additional cards may be added to a canasta to score their point values, but these do not affect the bonus - except that a wild card added to a natural canasta reduces it to a mixed canasta.

Other rules sources aren't as straight-forwardly clear on that point, but they say you can add to a meld on the table, and a Canasta is defined as a meld of 7 or more cards.