The blade is in Jakarta, you are always welcome to view it and in case you need to update yourself about Jakarta also.
I looked again the blade, may be you are right. Under proper sun light, the core is sandwich as normal, the middle line maybe an attempt as pamor or different type of material used (like sodo saler). The left darker colour is the core but none on the other side. The blade is welded tight and no visible joints.
I dont think any pamor here, just different material is being used and welded with the core.
thanks