Web update file diffs

Running 2 WebUpdate installer projects on the same set of files gives me an image which is almost exactly the same. To save upload bandwidth, I'd like to just upload one set of WebUpdate files and use them for both installers.

Running a binary diff, I see that in every file there are differences in the 6 bytes starting at address 0x12. What is the purpose of these 6 bytes? Will it hurt anything to use files generated by one installer with the executable from another, as long as only these 6 bytes are different?

We have done it once and it doesn't seem to have any obviously bad effects, but I have been seeing an increase in decompression errors #-200 and #8 on some end users' systems.