Just so we understand each other...
Example 1: You takeoff from airport A and fly 20nm to airport B and land. You takeoff from airport B and fly 40nm to airport C and land. It's 55nm, straight line, from airport A to airport C. You leave the plane at airport C and drive home cause the FAR's are so stupid. This trip does not qualify as a X/C flight for the instrument rating, in my book.
Example 2: You fly the above trip outbound but on the way back fly direct from airport A to airport C, which is 55nm, and land. I'm not completely sure, but I think this whole trip, all three legs, count as a X/C flight for the IR because one of the legs was over 50nm. It's a grey area for me because I've never done it that way before but after reading the reg, it seems like it's okay.
Example 3: You fly from airport A to airport C and land, which is 55nm. Then, you turn around and fly back from airport C, to airport A, and land, which, magically, is still 55nm. This trip counts, for sure, as a X/C flight for the IR. This is the way I trained and the way I train. I dare say, this is what the FAA expects and was the meaning and intent of the rule. But...If there are CFI's out there that are doing things differently and have the DE's blessing, I'd love to hear about it.