Lossy compressors don't have the same constraints as a lossless compressor. If you data your input, compress it, and then decompress it, the output is not identical to the input. This allows the compressor to potentially compress the data far more than even the ideal lossless compressor hypothesized above.
The question mark (?), also known as the interrogation point, query, and eroteme, is a punctuation mark that indicates an interrogative clause, or phrase in many languages. The question mark is not used for indirect questions.
A question mark is used to indicate that the solver must think in a non-standard way to solve the clue. Take for instance the clue should hard man have his head at last? for OUGHT. The wordplay consists of hard man (for TOUGH) but the T needs to be taken from the beginning and put at the end.