What is a lab pack?
Small containers of chemicals packed together into a larger container by compatibility class, so an accumulated inventory can be shipped and disposed of correctly. It is the usual answer to a laboratory, stockroom or closed-line cleanout.
We have unlabeled containers. Is that a problem?
It is common and it is workable. Unknowns are identified before packing, which adds a step but is routine, and it is a considerably better position than shipping them mislabeled.
Can spent solvent really be reused?
Often, depending on the chemistry and the contamination. Where reclaim qualifies it is evaluated first, because it recovers a material you otherwise pay twice for: once to buy, once to destroy.