We’ve purchased a RB411U with installed ROS V3.5 (L4) and had to upgrade to 4.5 because the 3G-Card was not recognized. Now the free upgradestep (+1) is lost for this board for future. 
Should we accept this, or is there another upgrade by goodwill of Mikrotik possible?
Why do you think that you lost an upgrade step?
What is your ‘/system license print’ say?
Ahem… Ok. It’s upgradeble to V5.x 
Very fine!