Not entirely sure how much more light I can shed on it.
Last time round, each segment did seem to come out quite distinctly - the 49ers and 44ers in the first week and then a batch of reserves, then closing ceremony segments and more reserves, then (from memory since no access to the spreadsheet here) the 47ers and more reserves. The only group that didn't have reserves on the following day were the 41ers although it was just afterwards that some reserves went astray. There was a theory then that you may be a reserve for a particular segment.
This time we have only had a few decisions and no reserves. We had about a 60% success rate last time whereas this time it is only at 20%. Not sure if that reflects that there is lots still to cast or that Olympic opportunities were scarce.
I don't think any of us thought in Jan that no reserve would be called up yet. It is beginning to feel, sad to say, that the reserve status may be a sneaky way to keep people onside just in case rather than giving an outright no. I greatly hope that this isn't the case though and that we do start to get some reserve promotions soon.