Points 1 and 2 address the two interfaces where management of unchanged values is advised.

2) Data Adapter to LS Server interface: unchanged values have a special treatment only in updates for items in MERGE and COMMAND mode (in the latter case, this only holds for the command==UPDATE case).
In this cases, unchanged field-value pairs can be omitted and the Server restores them internally and uses the correct values in updates and snapshots.
In the other cases, for field-value pair missing in the update, the value is considered as null for that update.

1) LS Server to Browser interface: this interface is internal to LS and it is managed in an optimized way.
In particular, sending unchanged values through the network is saved.
Then, on the Web Client Library to Application interface, the values for the unchanged fields are available.

Hence, you can try using a single item.
Anyway, it seems to me that you could have used two different items supplied by the same Data Adapter, without the need for using two Data Adapters.