As you click through TurboTax pages following the entry of these Forms 1099-R, I would expect TurboTax to prompt you to enter the explanation which will be included in your e-filing. Be sure to click the Continue button on the Your 1099-R Entries page and proceed through those follow-up pages as well. If for some reason TurboTax doesn't prompt you to enter the explanation statement (I think there are some scenarios where explanation is required but TurboTax does not prompt, but I don't think that this is one of them), I would manually prepare an explanation statement and include it with my mailed tax return.
