Under the circumstances, as you have briefly described them, I could see how you would have these questions. However, have you asked your lawyer to address them for you? I ask this because he/she is in the best position to discuss such an issue with you, given that he/she is more familiar with your case than any attorney on this website, and he/she was at the preliminary hearing.
This attorney is licensed to practice law in the State of California. The laws of your jurisdiction may differ and thus this answer is for informational and educational purposes only and is not to be considered as legal advice. Since all facts are not addressed in the question, this answer could change depending on other significant and important facts. This answer in no way constitutes an attorney-client relationship.
The truth or falsity of what the officer stated is not changed by whether the officer did or did not swear that the testimony would be true. It is fairly common for court reporters to make errors and not completely get down on paper everything said in court. The routine existence of mistakes is not changed by an opinion that the court reporters "know" not to make mistakes. Mistakes happen even when not intended, such as in a recent transcript of mine where I said the word "doctor" in the question, but the reporter put it down as "document." In another transcript I said "concrete blocks and metal pipes" but the reporter put it down as "concrete blocks, metal blocks." There is no reason to believe that the errors were intentional.
At trial, you might ask the officer/witness if he did swear to tell the truth at the prelim, and if he says he did, hand him an extra copy of the transcript and ask him to point out where in the transcript he did that. Possibly, when he is unable to do that, that could affect the jury's view of his credibility, but it is not clear it would have that effect.
Contact me at 248-399-6930 for a free consultation. You and I do not have an attorney-client relationship formed by our communications on this website. Advice given by me on this website is general advice based on partial information. You should not rely on any advice given without first hiring a lawyer in the area where the case is pending, and providing that lawyer with full information.