Mongo,  Bleeders were around in 1975.  I had a 5P which was one of the beginning series of what became yellow dot bleeders.  Mine registered out at 58 when hardness was measured.  it was considered as one of the better bleeders to have.  Originally had no idea what I bought but it turned out to be a great ball back then.  I have thrown it on today's conditions and it is not the ball it used to be.  Way too much oil compared to back then.  I was able to use it but the ABC hardness rule was going into affect right around that time period too.  There were other soft Colunbia balls back then too.  The real collectors balls in this category, soft or bleeders probably are certain versions of Crown Jewels.  They were out there earlier than any soft Columbia balls.

I wouldn't pay more than 35$ for a mid seventies bleeder, unless you want to look at it.  Mine has turned solid black from all the resin bleeding out and then the cover picking up dust and what not that then sticks to the ball.  Save your money...