The blade and lockbar are hand-fitted into each knife. They need to be swapped together as the tolerances are such that swapping just the blades is likely to cause poor fitment or locking, or perhaps just not fit at all. And that's delica to delica, or meadowlark to meadowlark.
Huge difference between them. Open both and look at the lock screw, where the lock and blade meet, etc, from the spine and compare. The Delica 4 lockbar is considerably longer than the Meadowlark 2.
Holy zombie thread, Batman!