After researching....
Discussion seems to indicate seeing 'stiching lines' on screen; sometimes in the designing application; or in the generated PDF. My instances are visible only in printing-in two of the four images.
1. Transparency. Is this an automatic occurence in generating the PDF? Can I turn it on/off? (The 'Save Adobe PDF' window that allows changes to: General, Compression, Marks & Bleeds,Output,, Advanced.....)
2.That same initial 'Save Adobe PDF' widow allows for three settings: Adobe PDF Preset (12 choices); Standard (6 choices), and Compatibility (5 choices). Note how the window signals a Warning (Warnings: Saving this file with Compatibilty set to Acrobat 4 (PDF 1.3) requires items with transparency to be flattened.) Could this be a warning that produces the stitch lines in the actual printing?
Thanks for your patience.