Reconvert with new DNG Converter?

Question

If I converted a bunch of Canon 7D CR2 files to DNG using DNG Converter 5.5, should I reconvert from the original raw file with 5.6? What is different about the files, since the raw data should remain unchanged?
I thought the advantage of using raw/DNG was that the file itself stayed intact and that, as raw processing algorithms get better over time, the data could be "crunched" in different ways to make the image better. I am getting a sense now that some of my DNG files created using older versions of the DNG Converter (I have been using DNG for several years now) are somehow inferior to those created using the latest version of the converter.
Any information on this issue is greatly appreciated!

Answer 1

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I do have the original CR2s, but say I had several DNG files created with 5.5 and then converted them with 5.6; since it is DNG to DNG, the original (inferior) 5.5 metadata is retained. This makes me feel like I have permanently "tainted" files because they were created with 5.5 (though I still have the original CR2s and could reconvert from the originals) and I am forever stuck with what I have
The current DNG converter does work this way, i.e. it does not replace that metadata (see the thread from Barry Pearson, requesting an option for replacing the metadata). Thus you would stuck with the incorrect metadata if you had not kept the CR2s.
Note, that there is no disadvantage of startiing out from the CR2, because the adjustments saved in the DNG file are not of much use anyway because of the changes. For example the color information has changed; I don't know how big the changes are, but they may require the readjustment of saturation and perhaps even WB. If you have ISO 100 shots (or 125, 250, 500, 1000 - but you should not use franctional ISOs with raw), then the image will become brighter after the new conversion, thus your Exposure, Fill, Brightness, Recovery settings may have to be changed.
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Will I get lower quality images from 5.5 DNGs than 5.6 DNGs?
Yes, but this is a speciality of the too quick and dirty support of the 7D in 5.5, i.e. this is not a generic consideration.
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Should I be more concerned about getting the latest ACR/LR and not worry so much about the DNG Converter version that was used to convert to DNG?
I have no idea if ACR 5.6 has any functional enhancements compared to 5.5. However, the correct support of 7D raw files in DNG format does not require 5.6 of ACR but of the DNG converter.
For example one of the problems with the preliminary support is the maze-like appearance on smooth surfaces in low ISO shots. The reason is a hardware fault (in cleartext: Canon created crap). This problem can be countered at least partly (I don't know if it goes away totally) with adding a certain metadata to instruct the raw processor to apply a somewhat different processing than normally. This is nothing new, even much older ACR versions do that - if the DNG converter inserted this information.
(The vertical banding in the very shadows of ISO 100 to 400 does not change, like http://www.panopeeper.com/Canon/Canon7D_Banding_ISO00100_Jehuty_DPR_0014.JPG)
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I am only nervous because I do not keep the original CR2s long term, only the DNG. I want to make sure that the DNGs I have created with 5.5 are not in some way inferior in quality before I delete the CR2s. If there is inferior metadata in the 5.5 DNGs, will using the latest version of ACR when it comes out "clean out" this bad metadata in favor of better processing methods, or is the only way to "clean out" the metadata to convert to DNG with the official release of the 5.6 DNG Converter?
As you have no way of making sure, that the conversion is perfect, it is foolish to delete the original, i.e. the CR2; the rest is speculation.
However, you should not discount the possibility, that another raw processor or another DNG converter (or a later version of Adobe's DNG converter) can make a better processing of the CR2 or a better conversion in DNG.
Gabor