Can cards from an invalid meld be used in a subsequent valid meld?
According to this answer to your previous question yes, you can use these in a valid meld. Here is the relevant quote:


  If a player exposes any cards from his hand, but does not meld them, he must leave them face-up on the table, and discard them one at a time in subsequent turns. However, if these cards can be validly melded before they are discarded, he may do so, rather than discard them.


As a side-note there are different rules and different variants of Canasta, and I do not believe there is one true way. That what makes difficult answering your question unambiguously.

For my Canasta games, I've written down my own version of Canasta rules, that I compiled from different sources on the web and got everyone at the table to agree to them. Since we are running a friendly non-commercial games, we simply re-deal the round if someone makes this mistake, because we trust that no one of us will do this intentionally. Anyway it happened only once or twice, so it has never been a problem for us.