Thank you for all that, it clears matters up. I have another thread on this in Photo Critique.
Layering of ISS pass - PentaxForums.com The interval thing bought me undone there. I was sure I was shooting the sequence in this thread with the interval set much less than the exposure time, but Subsequent attempts have seen me unable to replicate that. i can look at the originals and see exposure time, but the interval I was using is harder to pin down. Exposure time was 25 seconds, and i was getting 2 exposures per minute, according to the file info. I was perhaps using a 30 sec interval.
I knew I would get gaps, and the layering was going to give me stuttering stars, but I viewed it as a technical, learning exercise as much as anything. I tried a single exposure yesterday morning here
ISS pass in Western Australia - PentaxForums.com with less than optimal results. I am now thinking I should invest in the accessory GPS unit so I can utilise the Star Tracking on the K-70--this should give me steady stars and a satellite trail, at least up to the max of 5 minutes it is meant to work to, which certainly will cover any ISS passes.
For prediction, I am using an excellent app on my Android phone, ISS Detector , which also gives me Iridium flash timing. All information is there, including a visual Radar screen which works off your internal phone compass, and also an actual elevation dot which you match against the predicted track. I'll try some captures of that.
Again, thanks for your help.