Another option to prevent being unable to read older RAW files is to convert them to DNG. DNG is an open source RAW format created by Adobe, so all version of Adobe software, are able to read them. I have done that in the past until ACR catches up. I believe that the converter is built into Lightroom.
Lightroom can also make the conversion as the files are being imported. Many recommend do that, and not even using the camera format. It would prevent the problems you are currently having.