The rediscovery of the regional approach and of play-based evaluation has played a key role in the success of conventional exploration in new plays and frontier basins over the past two decades. In this paper, we compare the results of a vintage (1995) play assessment of onshore Colombia (Upper Magdalena Basin) with the actual results of exploration over the following 20 years, reconstructing the vintage risk assessment and recomputing yet-to-find (YTF) using different methodologies. The overall perception of chance displayed on the vintage play maps proved to be largely correct, with most of the discoveries made over the following 20 years being within the forecasted ‘sweet spots’ and the higher risk areas being confirmed by the subsequent, less successful exploration drilling. In contrast, the YTF calculated in the vintage evaluation was overestimated. Such an overestimation of YTF seems a persistent problem in the exploration and production (E&P) industry. Recreating and analysing the vintage assessment in light of subsequent exploration results highlighted that field size distribution (FSD), the number of future accumulations and the prospect-specific risk evaluation were the main variables responsible for the overestimation of the YTF. Clearly, calculating reliable YTF is only possible with sound geological, exploration and statistical knowledge of the analysed play.