According to Wikipedia, Bullpen V2 is not used in 60s,70s,80s
http://somonline.wikia.com/wiki/Bullpen_v2So, when Koufax of the 60's pitched in relief after resting for only two games after his previous start and comes in as an F9 instead of a partial or fully fatigued pitcher, it's either because
1. He's a starter/reliever, rather than just a starter.
2. He was assigned a role as a LH specialist
3. He threw only 68 pitches in his prior start.
4. Bullpen V1 has custom code for just Koufax.
When Buchholz comes in to relieve after starting the previous game because HAL ran out of pitchers, and comes in as an F0, it's either because
1. He is listed as a starter only, so he wasn't assigned a role.
2. He is controlled by Bullpen V2, which has different rules than the Bullpen V1 of the 1960's player set.