Of course, I know that some race formats were more likely to have that happen, but the BL 13-heat format (with Heat 2 as the reserves race) made it much more difficult. I did find a BSF post from a few years back where somebody stated that it was "impossible" to have that post-1968. However, it wasn't impossible, but it was impossible for the three heat-leader positions (it could happen with positions 2, 3, and 4).
Obviously, I don't want anyone to devote their lives to looking for stuff like this to help me (not that old-time speedway fans like us have a life ), but I certainly appreciate everybody's efforts!