DoctorLarry: Perhaps you can offer at least one of the "many other possible explanations" for them to get equal clubs for my enlightenment.
That's a bit hampered by the fact you weren't talking about the op and I've no idea who you are talking about, but I'll use the op to illustrate one for you. It takes a bit of work and I'm a touch peeved at your attitude so you'll get the one you asked for and that's it.
Simply put there is a difference. The op was gifted the p970's yet soon after (on the 25th) bought the apex 19's, which are slightly cheaper and available five levels earlier. On the face of it a bit odd. He loses yardage and spin but gains a slower meter.
About the same time he changed from the Max balls to the L95 TP5, these gave him more distance and spin but a faster meter. He couldn't handle the meter with the p970's and the better balls so thought the 19's with them may be a better combination than the 970's and the max balls. I think he's now on to the the 19's and the max balls.
People want different things and sometimes it's a combination of clubs aand balls that get the right balance between hitting the ding and getting enough distance and the right spin for them.
Or more simply he dumped the p970's and got the 19's as he couldn't handle the meter or the former, he thought he could when he asked for them but found he couldn't.
Just in case it's a problem that I moved the question from equal clubs I was assuming equal didn't mean exactly that as I doubt if there's such a thing in the shop (I've not looked).