Yeah, the only time you see a clogged filter is after a major failure. But the thing is, you don't know what the "chicken" was. If, in the course of normal operation, the filter partly clogs and restricts flow, the trans could begin to slip. Just a little at first but it would then start dropping more debris, which would then get caught in the filter, further restricting flow and... well you see where I'm going here. It would be difficult to discover the root cause.
The thing is.... according to the decades of work Eleftherakis and Khalil did studying AT filtration (which you can get at the SAE store)... the average range of sizes for "normal" wear debris in an automatic is 5-15u. That stuff will pass right thru even the best 60-80u pan filters that are out there now, never mind the 100-150-200u screens of the old days.
I think it might be possible to clog a 60u filter with oxidative byproducts from excessive heat but I suspect the trans would fail in some other way before teh filter would cause it to fail.
Excessive amount of that size contamination will beget more and more debris, more and more wear and it will eventually kill the trans. By the time the big stuff comes along to clog the filter, the trans is already severely enough damaged that its on borrowed time anyway.
So, and y'all can check my logic here because this thought just occurred to me, it seems that it really isn't possible to plug an in-pan trans filter in normal circumstances, without some other major failure taking place first. I can invent some scenarios where it might be remotely possible, but the vast majority of the time, I don't think it would.
From my reading, and a coupla great conversations with Abe Khalil, it seems prudent to change the filter and clean the magnet in the pan short after break-in is achieved, because the trans generates 75 percent of it's lifetime of normal wear materials within the first 5K miles. That comes from break in as well as the contaminants that're built in during manufacturing. After that, it would seem safe to me the let the pan go... at least over a couple of OCIs, if not the remainder of the transmission's lifetime. Without knowing for sure, I would probably change it just for observation and learning reasons but my semi-WAG now would be that it basically can't clog without other things happening first.