The images that are included in the data delivery package may not include all spectral windows, or all channels, or all targets that were observed as part of the science program. These images are meant to be representative, as described in Imaging Products section of the Quality Assurance Goals section of the ALMA Technical Handbook:
"The ultimate goal for ALMA QA is that the delivered products are considered "Science Ready", suitable for publishing with little need for the user to reprocess... users may need to invest their own time and expertise to ensure that the data products are suitable to meet their science goals."
Investigators should expect to need to re-image their data. In particular, care should be taken to optimize continuum subtraction (if relevant) and fine-tune the image deconvolution parameters (e.g. clean masks and thresholds).
For a comprehensive guide to the imaging pipeline, please refer to the ALMA Pipeline User's Guide. Bear in mind that most ARCs and ARC nodes encourage data reduction visits if you would like help with improving your images. How do I arrange a visit to one of the ARCs?