📝 Ply starting or actually de-laminating. What to do?
As you know, I am a habitual restorer of basket cases that any sensible person would avoid like the plague - and I have come across and dealt with this same problem many times before..
The first thing you need to do is to get your nice dry de-laminated plywood wet again - and give it time for the moisture to soak well into the wood.
While that is happening sort out something like a couple of hardwood or alloy plates that will fit against both outside faces of the delaminated bulkheads and some clamps that are deep enough to press the sandwich of plates and bulkheads together.
Now wipe the wetted wood with a kitchen towel to remove any excess moisture.
Inject some good quality water-proof PVA taking advantage of the now plyable wood to get the glue right down and between the different layers of delaminated ply. I save any thin slithers of wood that are left over from the bandsaw to help with spreading glue in tight areas like this.
Use plenty of glue as when the plates squeeze it together any excess will get pressed out - and also into the small areas that you were not able to reach.
Wipe away any excess glue as it is forced out of the wood with a damp cloth.
Keep the plates under firm pressure for at least 24 hours and when removed the bulkhead should be flat and stay that way.
Hope this helps,