Another blog post. I thought I'd just give out everything I know about the different Japanese releases of the main manga, but because a lot of this consist of "I don't know" and "I guess" I didn't want to create an article about it yet.
(The version on Mangafox is either the 1972, 1978 or 1993 one, except the covers and short chapters at the start of volume 1 and 2 which are from the 1987 editions.)
The ISBN of every version up to the 2008 one, except 1978, are on Wikipedia.
1972: 5 volumes. Most likely only black and white. Volume 1 cover art: 
1978: 5 volumes. I know nothing else about this version. But it is unlikely to be any different from the original, apart from maybe the covers.
1983: 3 volumes. These appear to have been released with a matching Shin Deviman volume, making it unlikely that these editions incorporate Shin Devilman into them. Contents are very likely to be identical to one, or both, of the preceding. Cover: 
1987: 5 volumes. A few pages have color. According to what I've heard this was the first release to incorporate Shin Devilman (in vol. 3). It is also the first release to include Great War of the Gods, the Sirene chapter, One Summer Day and Fallen Angel, in volume 1, 2, 4 and 5 respectively. Hardback. Vol. 1 cover art: 
1993: 5 volumes. Looks identical to the 1972 version and is likely an identical reprint.
1997: 5 volumes. Unique covers. A paperback reprint of 1987. Cover: 
2000: 3 volumes. I said in an earlier comment that this looked identical to the 1983 version. I appear to have been mistaken. Cover: 
2000: One volume omnibus. 30th anniversary edition. Is very likely to have the same content as the other version from the same year. 1000 A4 pages. Hardcover.
2002-2003: Bilingual version. 5 volumes. Appears to be black and white only. Shin Devilman is incorporated. And includes addition: new double splash pages for vol. 5, chapter front pieces and an new, extended conclusion for the Zann story in vol 3. Most likely a reprint (apart from the translation) of an earlier version with the same inclusions. Cover: 
2004: 3 volumes. Cover looks like those of the 1983 version, but with additional text. I have no idea concerning their content, but unlike the '83 editions they do not appear to have been released with a separate Shin Devilman volume, making it possible (but not guarantied) that they incorporate it. Cover: 
2008: One volume omnibus. Have the same artwork on the cover as volume 3 of 1983 and 2004. Probably reprints another recent edition. 1000 pages. Cover: 
2009: 4 volumes. "Refurbished edition" (新装版). I know nothing about it. I think one review I read said that it is identical to the 2012 version, but I might have misunderstood him. Cover: 
2012: 4 volumes. "Revised edition" (改訂版). Minor changes to artwork. Like so:  and so: . Because it does not try to be as close to the original as possible, it is unlikely to be based on a version without additions. Cover: 
My guess as to what is going on here is that the versions prior to 1987 are probably identical. After that version most releases copied it, probably adding some new content of their own which later version in turn also included (I hope). The Bilingual version is one of these. Some versions, like the 1993 one, however copied the original release for authenticity/artwork-consistency/nostalgia. And the 2009/2012 version changed some of the the artwork, most probably from an 1987 based version.