At present, there is a distinction between:

• zPatch.esp
  • Patcher 1
  • Patcher 2

and:

• zPatch.esp
  • Patcher 1
• zPatch2.esp
  • Patcher 2

The difference being that if Patcher 1 adds a new record, in the first scenario, that record will not be visible to Patcher 2, while in the second scenario it will not.

This is arguably a bug, as the documentation suggests that there should be no distinction between the two scenarios, other than the second one consuming two entries in the user's load order.