I would sell you the book, if it existed. The problem is that it would probably be obsolete before you could finish reading it. Well, maybe not completely obsolete, but things have changed in the mortgage industry since last spring.
We used to get daily rate sheets showing the interest rates for various lenders under all their programs. Last year we were getting daily rule change notices. It was pretty hectic trying to keep a loan together while it was being processed and the rules were constantly changing. Now the rules have pretty much stabilized.
I don't know of a single lender who uses Vantage.
The three big bureaus that Sera mentioned offer scoring models with different names. Experian uses the Fair-Isaac (FICO) model, Equifax uses the Beacon model, and TransUnion uses the Empirica model. All of these models have variations as well, like Fair Isaac 1, Fair Isaac 2, Beacon 5.0, Empirica 95, Empirica 04, Empirica 98, etc.
Scoring models take the data on file for what happened when, for what amount on what type of credit account, and crunches that data into a score, usually between 350 and 830. Most models weight things that happened recently far greater than something that happened 2 years ago. Housing-related issues, like utility collections or rent liens or mortgage lates are weighted differently from credit cards. The number of accounts is a factor, the amount of credit utilized out of a maximum authorized is a factor, the lateness if any of payments is a factor and so on. There are just a lot of ways of looking at the same data. Most of the 3 bureaus have the exact same data, (but some have additional reported problems from the others).
As to which model is used, lenders have different methods, but the vast majority look at whatever score is between the other 2 and use that 'middle' score to determine your basic eligibility. The other two scores are not normally thrown away, and any issues reported from those bureaus may be examined by the underwriter.
So, to answer your question about FICO -- only Experian actually reports it, but the others have equivalent models, and they can also calculate the FICO. They're normally reporting Beacon and Empirica. The Fair-Isaac model treats the data a particular way, which is different from Beacon and Empirica. Vantage is a whole different animal, not used by lenders. We wouldn't be able to equate the scoring model of Vantage to FICO, since every bit of data is weighted differently -- we'd have to know the data points, too, and the model would have to be public. The models are trade secrets and protected from disclosure by law.
If you want your real scores that would be used by a lender, ask a loan officer to pull them for you. Most will not charge you for this, even though they must pay for each pull.
Q1 - Now that you realize the 'middle' score is used and it must be above 620 for most lenders -- this is often the minimum -- there are lenders who will not look at the number, but rather make a judgment based on your data points (individual reports from all your creditors). FHA, VA and USDA actually don't refer to numbers, only the lenders who get those guarantees from those agencies actually impose credit score limits.
Q2 - None of the 3 major or the 1 less well known bureaus has any more weight than the others.
Yes, it would take a book to describe all the subtleties in credit scoring, but these are the basics.
Be aware that a score below 640 but above 620 can actually cost a higher interest rate than a higher score. Here we're talking middle scores. Some lenders place a penalty on the rate when the score is above the minimum but not by much. This is typical for FHA lenders.
On the other hand, conventional lenders are even more strict, and generally any middle score below 680 takes a hit. The private mortgage insurance also takes a hit, i.e. it's higher the lower your score. If your score is low, you might also find the lender requires a higher down payment to reduce his risk.
In this little space we can't possibly write down all the interactions and caveats.
If you want to shop, ask your loan officer to pull your credit and ask him what the rates are. Ask him for a copy so you can see what's on your credit report. If you have problems, months before getting a loan is when to fix those problems, not 30 days before closing. Sometimes problems can be fixed quickly (in less than 30 days) but it does cost extra and is stressful for the borrower who just didn't know about it beforehand and now has to pay money to clear an account. This is the case when you don't have time to argue with the creditor about what happened -- you just have to pay them off.
I hope all this helps. If you have specific things you'd like to know, just send me an email.