Fully machined into 2 sections means one plank instead of being full lengths like the others, it will be made out of 2 pieces.
These 2 sections normally helps the fitter when they start and/or finish the raw of fitting.
If the length is 1900 mm, all planks (A) will have a length of 1900 but the last one (B) will be made by two pieces, one of 1300 mm + one of 600 mm.
(B) plank might also be split into different length i.e. 1000 and 900 or other.