Sorry for the delay in thanking you for your responses. I thought I was set to receive notices of replies but apparently I wasn't.
To the first response: Pinholes, when discussing film, are tiny spots where the film is damaged and clear. They can appear similar to film that had dust on it when the film was exposed. They are usually caused, at least in my 45 years of experience, from the sudden change in alkalinity when film goes from developer to an acid stop bath. This usually isn't a problem but I remember reading long ago that Ilford films were (at that time, anyway) prone to pinholes and I even experienced what I believe were pinholes years ago when I used some Ilford HP5+ sheet film. The only time I have ever experienced pinholes was with Ilford HP5+ sheet film long ago so I was watching for it this time. I noticed them when I was reading density patches with my densitometer while doing testing which I just finished today.
I do use a water pre-soak for all my b&w films so that's not an issue. Also, I can't see why pre-soaking or not pre-soaking would have any effect one way or the other with pinholes. It's my understanding that pinholes can be caused when gases are released from the emulsion (in some cases) when the film goes from the alkaline developer to the acid stop bath. When I experienced this years ago, I did some research and what I came up with was that Ilford films (at least HP5+) can be prone to pinholes when an acid stop is used.
I don't like to use a plain water stop because I like an abrupt development stop and also I want to avoid carryover of developer to the fix.
I have contacted Ilford technical support about this but I haven't received a response yet.
I just completed my calibration testing so I'm going to check out one other possibility. I do my Zone System testing by placing a Stouffer's step wedge over the film in the holder to get 31 (actually 33 because I modified the wedge to give me DMAX and fb+fog readings) exposures on the film with a single camera exposure. I'm always very careful with my film so I virtually never get dust on it (see my videos on YouTube to see how - look for videos by Tom Johnston or ZoneIII). However, my step wedge gets a lot of handling so there's a slim possibility that I may have had a little dust on it. Also, there are three surfaces involved that could cause what might appear to be pinholes if dust were on one of them. Now that I'm done with testing, I'll check that out but what appears to be pinholes on the film are not in the same locations on each sheet of test film. I really doubt that that's the problem, though. I have never had this happen when testing any other film.
So, for now, I'm going to reduce the concentration of my stop bath. I was just wondering if anyone else experienced this. It is (or was) a known problem.
Again, thanks for your responses.