However, what I'm wondering is, some units that don't have this 'paradrop' checked are also being dropped by parachute or glider as airborne reinforcements.Paradrop – unit is capable of being dropped by parachute or glider. Depending on their training, this may or may not apply to all Parachute units.
Below is an example from the 'Market Garden' scenario in Scheldt '44 (Scheldt_44_September.oob).
The 3rd parachute battalion under the 1st Airborne Brigade of the UK's 1st Airborne division has 'Paradrop' checked as shown below. If you run pcedit.exe to load the 'Market Garden' scenario, select the above unit in the 'Scheduled dialog' and click the 'Modify' button, the 'Reinforce dialog' window will pop up as shown below, and you can see that it is scheduled to arrive as reinforcements by 'Paratroop'.
On the other hand, the 1st Airborne division HQ unit does not have 'Paradrop' checked as shown below. As above, when you run pcedit.exe, you can see that it will arrive in the form of 'Glider' reinforcements as shown below.
This means that regardless of a unit's 'Paradrop' capability, it can receive airborne reinforcements by Parachute or Glider.
Units that are airborne reinforcements will only arrive as reinforcements by Parachute or Glider once in the scenario. It is not possible to paradrop a second or third time from the airfield again during the game. Therefore, I wonder if the 'Paradrop' capability in the 'Org/Unit dialog' above is almost useless in the game if it does not even serve to limit airborne reinforcements. If I'm wrong, please correct me.