From time immemorial (2012) the PPP Top 25 Under 25 has used one tabulation method to figure out the final rankings. (As far as we know, no one can really remember.) That method was to weight all the unranked votes at 100 and then just average the votes.
This method hasn’t been too popular lately, and the difficulty here is simple: Either we force every voter to rank the entire list or we weight unranked votes somehow, it’s merely a question of how.
The very good reason to not do the full ranking is because I don’t wanna.