There is alot to an approval-
Many lenders eliminate applications based on criteria-
BK, paid CA,unpaid CA, # of inquiries, UTL, # of derog payments in 2 years. ETC
Then it is about minimum score and Debt to income, and sometimes how they are feeling that day.
As far a Credit lines- sometimes they are alot higher that expected sometime really low, sometime they match the highest- lord knows how they come up with these things.
Some use a PFICO (bankcard enhanced score) and many use their internal scoring system (Amex)
I hope this helps.