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Ahá! Thanks!

I summarize here what I've read from links you have posted here, to other interested people who may visit this thread:

"RPM needs to be able to determine which version numbers are more recent than others, in order to perform its version comparisons. It's pretty simple to determine that version 1.5 is older than version 1.6. But what about 2.01 and 2.1? Or 7.6a and 7.6? There's no way for RPM to keep up with all the different version-numbering schemes in use. But there is a solution: epoch numbers.

When RPM can't decipher a package's version number, it's time to pull out the Epoch tag. This tag is used to help RPM determine version number ordering. If a packet has an epoch number of 42, what does the 42 mean? Only that this version of the package is newer than the same package with an epoch number of 41, but older than the same package with an epoch number of 43. If you think of epoch numbers as being nothing more than very simple version numbers, you'll be on the mark. In other words, Epoch is the most significant component of a package's complete version identifier with regards to RPM's version comparison algorithm."