Critter-3 is incorrect about ignoring any codes. There is no weighting between codes, the payer is permitted to list the appropriate codes in any order. In the cases of the IRRs that you described, the code G is the correct code.
Each code has a specific meaning, but some combinations are not permitted because they have incompatible meanings. For example, code 7 implies a distribution paid to you while code G implies a rollover paid directly from a qualified retirement plan to another retirement account, not a distribution paid to you. The IRS has no way of knowing which of these codes describes the transaction when they are incompatible with each other, and there could be a taxable difference depending on which code actually applied.
In most cases, if an incorrect Form 1099-R has been prepared by the payer, the payer must make the correction. If the payer refuses to make a needed correction, there is the option to file a substitute Form 1099-R (Form 4852) with the correct information, but doing so would preclude e-filing.
