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Another disadvantage of F-111 is that it will wear out faster than ZP.

How do you tell when the PCs in BASE are wearing out?

"OK, now the easy part. If you want your pilot chute to always function properly, simply make sure, in the inflated state, that no part of the skirt is above the apex. In other words, make sure neither your centerline nor your kill line is too short. I pulled the apex on my hand deployed pilot chute for two reasons. 1. It makes them open faster. 2. It yields 11% more drag. However, IF THE APEX IS PULLED DOWN BELOW ANY PART OF THE SKIRT, THE PILOT CHUTE WILL NOT FUNCTION PROPERLY.

How do I check that? First cock you pilot chute like you would during packing. Now hold your pilot chute UPSIDE DOWN by the bridle at the base. Simultaneously pull downward on the apex (handle) and each support tape where it touches the skirt. The apex should be equal to, preferable slightly "below", but never "above" the skirt. (Please remember, the terms "above" and "below", in quotes, refer only to the "upside down" pilot chute you are holding in your hands for this test.) Now look how your support tapes are sewn to the mesh. If they are sewn "on the bias" your pilot chute is properly constructed. If they are not sewn on the bias it means that the mesh halfway between each support tape IS on the bias and will stretch more than enough to allow the skirt to get way "below" the apex. Try it. It's like a round parachute with several different line lengths. It simply doesn't work very well. This extremely common construction error might not let your pilot chute fully inflate, or in extreme cases, inflate at all. If your pilot chute is "borderline" when it is new, then things will get worse and worse as it ages.

Let me see if I can get some manufacturers to comment on this one.

There are no "set" retirement numbers for PC's.  Like a canopy, when you notice decreased performance, it is time to retire them.  Trying to blow air through the fabric is the best test to determine the porosity of both a canopy and a pilot chute.  The advantage to ZP, is that the fabric maintains the same "lack" of porosity for a much longer time than F-111.  The problem with an F-111 pilot chute, is that you really don't notice the lack of pull force until you have a hesitation.  Hopefully this is on a jump which will allow you this hesitation, obviously.  The vented pilot chutes are great because you get the longer life span of the ZP with the benefit of a consistent airflow through the apex, jump after jump.

Gardner made the point about PC trim. This is probably the most relevant. Fabric porosity and strength will degrade through time.  In part because of use cycles but largely due to handling, UV and dirt exposure.

There is a threshold when your PC is more likely, or even prone, to structural failure due  to these factors. However, much sooner than that will come the issue of trim.  Through use and or other factors (water for example) pilot chute materials, load tapes and the centerline can change dimensionally.  When this happens the PC has potential to lose performance or begin to behave erratically.

So.... when to retire?  Some people do it on a schedule. This makes a lot of sense. Think of it as routine, preventative maintenance. We all do it on our vehicles.  We change the oil on regular intervals rather than wait for failure.  75-100 jumps would be about right.

The degradation will occur gradually so regular inspections won't reveal a little red flag that says "replace me now" .  There are some markers that can be observed that will let you know things are degrading. When the symmetry of the pilot chute load tapes begin to decline is a good time. About 2% (or .50" on a 42"PC) is when things will get weird. Also keep an eye out for stitch holes in the fabric fatiguing, especially near the apex cap.  Pay attention to the centerline attachments and the main (circumferential) seam.

Retirement for ZP vs F-111?  ZP will last significantly longer but when it goes it's likely to go big.

It should be noted that most contemporary PCs are so over built that structural failure is not so likely.  Through time, degradation of performance and reliability become the factors.