This is on a Deere 30,40, 50, 55 series quad shift. One lever has 4 gears labeled A< B< C< D and Park. Must use clutch any time moving this lever.  The second lever is labeled R1, R2 1, 2, N, 3, 4.  No clutch needed when shifting between 1-2 any direction or 3-4 any direction or R1-R2 any direction. Must use clutch when going between 2-3 which is between the N and also any time you shift to R1.

Just think of the quad as adding a two speed, shift on the go unit in front of a syncrorange.  Like a TA on a red tractor but not as big of speed change.  The other thing is the gears don't 'lay out nice'  C1 is between B1 & B2,  B4 is between C 3 & C4 etc.

I had a 4440 with quad range that I purchased new.  I found it to be an awkward transmission even tho there were more gears.  Much of the time I wound up running in C1 and the reverse in that range is too fast to back up if you need it at the end of the field and no way of shifting down also approaching the end of a field.  I did learn however to shift on the go between ranges using a foot throttle and no clutch, but that wouldn't work if there was much of a load. Used it that way on a grain kart for several years with a straight pipe and shifting it like an over the road truck.  Was fun at times, but to teach any hired help to do that was hopeless!  A powershift trans or even the synchro range were better choices.