The small ones came from the west side of that water course we had to deal with during the walk. (49.11054, -123.908747) You posted a map on page 149 of this thread. It shows a stream from Beck Lake heading north. Southfield No. 2 slope looks like a good candidate.
Ya, as much as I would like to believe we found a Black Track splice bar, the scenario you describe is the more likely. But, the darn thing laid in the bush for close to 100 years in any case!
Scambling up the bank after being stopped by water covering the trail, we saw Milepost 68. The splice bar was just north of that, perhaps 68.1 or 68.2. The Black Track went under the E&N at Mile 68.8. The trestle at that location was filled during the 70s.