I bought a used Meade LX90 and the manual that came with it says ACF on it but the telescope itself does not say ACf anywhere on it. The question I have is do ALL LX90 with ACF have it printed on the telescope or were there some that did not have it printed on them?
Not all LX90s had ACF optics, when they first came out they were standard. It wasn't until 2009 that Meade switched production for LX90s to the ACF optics discontinuing the older classic optics. ACF designation in the manual may have nothing to do with your telescope itself, as ACF pertains to optics only. Look at the corrector retaining ring to see if there is an ACF on it. You could also take the plastic cover of the Dec arms and see what the PCBs are dated, If they are 2009 or newer you probably have the ACF. Another test would be to use a low power eyepiece and observe the outer edge of a starfield for coma.