Oh the complexities of wheel building !!!!
I went to build a Matchless back wheel on Thursday, I had stripped the wheel myself and measured the spokes, inner and outer both sides 206mm, got a new rim and spokes to fit and it wouldn't lace up, the spokes were too long for cross two and too short for cross three.
I resorted to an on-line spoke calculator program which told me cross two required 200mm spokes and cross three 212mm, I had some 212mm spokes, used those and it laced up correctly.
How could it have had 206mm spokes in it before ??????