I don't have the newest edition, but in general...
2. I seem to miss one Dragon counter and one Sagger counter compared to the OOB. Is this going to be a problem in some scenarios?
Check on the back of other support weapons and you'll prob find the "missing ones". If you find them on the back, you should not have any issues in the scenarios.
3. The US TOW Jeep and Chaparral have no unit designation. Does this mean these units are unattached?
Correct - they can be used by any US formation and will be called for in the scenario.
4. Why does the HIND units don't have a unit designation? They are attached to the 69th AHR, right?
5. The 81mm Mortar don't have a unit designation as well. Is this unit part of the 2nd Airborne, as stated in the OOB?
Yes to both. The counters in my older edition are marked properly for their formations.