I too have one example of a Prexie coil paste-up. It too was done at the joint line (Note the trace of a line on the perf tip at the top.) I agree these are very uncommon, as opposed to finding Prexies with the start/end wrapper portion attached.
I surmise the splices in these near-finished coils were done at the joint lines to make accounting of the scrap easier. Every piece of scrap would be the same size/value.

