I thought rescues spayed and neutered dogs before adoption what is this world coming to!
You determine bloodline by looking at what the predigree is comprised of. If you're dogs are rescues / not registered then you can't know the bloodline.
I would do a lot more research people will tell you all types of misinformation. To produce tan point a dog doesn't need to be from old bloodlines. Both parents simply need to carry it. Literally it is potentially possible for a Lab x Pit Bull to produce "tri".