New to me Andy.
Does this person have anything in print that indicates this? The SL500 from day one supported LTO2/LTO3 and SDLT. There is a difference in the size of the arrays, so you need the correct type of base/expansion units (LTO or multimedia) but the SL500 compat manual has no mention of different types of robotics assembly for LTO or mixed LTO/SDLT.
Still, I've been wrong before...