Typically if you reaffirm the loan would start to report again. If you don't, it doesn't.
Don't let that factor into your decision to reaffirm. IMO it should be avoided at all costs so long as your lender doesn't repo if you keep making payments.
You can get an installment loan reporting on your credit (if the car was your only one) with a self lender loan.
I honestly wouldn't bother looking at your scores or thinking about disputes until 1 month post discharge. Just about everything will be reporting right by then and you save yourself a lot of unnecessary headaches. Focus on researching and getting yourself on a good budget during this time.
Here is what I did. Others may disagree.
The day after my section 341 meeting (30 days after filing) I submitted my bankruptcy papers to each of the CRA's and disputed all the IIB accounts as needing to be updated to "included in bankruptcy." This is the standard notation whether or not the bankruptcy is discharged or not. All my bankruptcy creditors updated my balances to zero and worte "included in bankruptcy." I realize the BK was not discharged and I could have not gone through with it, in which case they would have later changed it to a regular chargeoff. This had the effect of getting ALL of my accounts down to a zero balance immediately. Because I had owed $100K in debt and now I as showing $0 in debt, my scores went up a good 50 points before discharge. Also a few of my included in bankruptcy reports actually deleted with this dispute. At the same time I opened a credit builder share secured loan at my credit union (BECU). They don't do a credit check so that went through and reported immediately. I also opened an OpenSky Visa credit card for $200 since it did not involve a credit check. I opened both of these accounts with the approval of my BK lawyer who is one of Seattle's best and most active. He said I could open any secured cards that would take me though many would still reject me with an undischarged BK. So the very lowest my FICO scores reported were right at filing date and then they only dropped like 20 points because they were so low already from high utilization and being so far past due. I braced myself for another big hit the day the discharge hit my reports and oddly that event did absolutely nothing for my scores. I expected it to further lower them.
So by the time I reached my discharge date, I had no balances reporting except a small balance on my open sky secured Visa. I had my small $500 credit builder loan (reporting almost $500 owing on $500), and I had zero balances showing for the IIB accounts and all of the IIB accounts reported zero balance and IIB (and had for months).
Because of this I went from about 525 to 625 the day my discharge filed. I then was able over the next six months to open three regular unsecured cards. My scores quickly shot up to the 660s.
Others will tell you to wait. I disagree. But we each share our lived experiences.
As far as the car loan, if you reaffirm, it will start reporting again and will show you as X number of months behind at the point of the BK but will then show you on time if you pay on time going forward. If you do not reaffirm, some lenders like Capital 1 will let you keep paying and won't repo you. This is what I did. My lawyer had a feces fit about my wanting to reaffirm that loan (I only owed $2K on a $10K car) and I wish I had done so but he made it sound so bad that I didn't. He was doing his job as a lawyer, knowing I could walk away from that car at any time without any further credit damage, so he was right in that sense. But I only had 5 small payments left and I could have gotten credit for them and my reports would look better today without that auto IIB and showing as a write off, even though I paid it off on time and never pissed a payment.
Hope this helps!