Refurbishing a centerboard

Two friends and ! are refurbishing two 2500 series boats.  We intend to make them available at very reasonable prices to entice new club members to come and sail with us on Lake Monona in Madison Wisconsin.  One centerboard we are repairing is different that others that I have seen.  There is a seam in the glass perpendicular to the length of the board about half way up the board.  It won't make any difference to our repair but it is puzzling.  It seems that when laying up the board the cloth would be  installed length wise rather than two pieces crosswise as you can see in the picture.  Has anyone seen this before.  This board is from a Douglas boat.  I would call Harry and ask but we have bugged him enough with questions on these project boats that I will feel quilty until we buy some more parts from him next spring  :-)           

I wonder if there is/was an abrasive material in the centerboard well being used to shim it?

It's not a seam.  It's where an edge of the lead part of the centerboard is located.  They probably added additional glass there to support the transition to the heavier part of the centerboard.
Looks like the paint has been scraped off a bit in that area.
Repairing the CB is pretty easy.  Fire away with questions...