B777 First Officer reported there were errors on the Final DG form and after departure; realized that the flight crew were no longer in compliance with requirements due to the lack of information that should have been included on the DG form.

Narrative

After ACARS initialization; we received the primary Dangerous Goods (DG) information; consisting of a Planned DG Summary and expanded information for each DG item. The Planned DG Summary showed a total of 28 planned items; and although loading had not yet been completed; the position information for each item had been populated. Items 1 - 4 were shown in the aft pit; items 5 - 24 were shown as being held off; and items 25 - 28 were in the forward pit. We received the Final DG information prior to pushback and departed normally after sending a DG acknowledgement code.After departure; we determined that the expanded DG information for item 1 was not included with the Final DG report. We also determined that the Final DG information did not include a new DG Summary. We could therefore not determine whether item 1 had been held off; although plan be in the aft pit; or if we were missing the expanded information for the DG item. We sent a DG acknowledgement code; which returned only the expanded information for each item - it did not include the summary. We therefore also determined that if we had followed the new FOM guidance and had thrown away the Planned DG information; we would no longer be in compliance with FAR and ICAO requirements; as we would not have the information included on the DG Summary form; e.g.; pit location.