In turn 63 of this battle and turn 58 of this battle, there were stats that didn't go higher even though they were below +6. Why does that happen?
It is because in RBY and GSC, Pokemon's stats were maxed at 999. Even if you could still 'boost' the stats up to 6 times, it would roll over to zero again.. It wasn't until RSE that they could go higher than 999.