The photos are uploading but we'll need more that close-ups of the serial number. However, I do see what appears to a brazed-on kickstand plate, which would typically indicate a low end model. Also, it has a plastic cable routing guide under the BB shell, which typically indicates no earlier than mid-1980s. Finally, there are huge blobs of brazing material at the junction of the BB shell and down tube, so it doesn't appear to be lugged but it's also not TIG welded. That would place it 1980s and, based on the two S/N numbers, likely a circa 1985 model. I haven't seen P-codes on Bianchi in the past. One manufacturer that used P-codes was Pacific Cycle, a Taiwanese manufacturer.