When filing delinquent returns when you want to file an offer-in-compromise, do you send the returns with the OIC, do you file the returns with the RO, do you file at the address in the 1040 instructions, or do you do all 3?

You should file the returns as follows:
a. If working with a Revenue Officer, file the returns through them but include signed copies with the Offer package so the Centralized Offer Unit knows the returns were filed and actually have signed copies in case they need to process them,
b. If you are not working with a Revenue Officer then file them per the return instructions. If they can all be e-filed, then e-file them. If you have a mix of current that can be e-filed and older returns that cannot be e-filed, then I recommend filing all of them by mail in one package, so they all get opened, processed and assessed together (see Question #7 above).
As far as the Offer you and your client are eager to get filed, the Offer unit will first check to see if the taxpayer\’s returns are on file and assessed. If you are concerned they will not be in the system, or even if you are not sure if the returns will show up in the IRS system, I would include with the Offer package signed copies of the returns and explain that they were filed but you are including signed copies so the Offer Unit has them. This should avoid having the Offer Unit return the Offer because they do not see the assessed returns in their system.