Danny is right, but I believe there is also a second reason. El Al is not allowed to fly on Sabbath. An orthodox Jew seeing El Al in the sky on that day would go nuts. Since Sun d'Or is not restricted the LY
titles are removed.
Also the CAL 747's had their titles removed to be able to haul cargo 7 days a week. Nowadays they leave 'm white, just as simple.
BTW, also saw 4X-AXQ at AMS
on Oct. 17, old c/s, without titles.