If 8u25 existed on the system, one can not invoke the 8u20 online installer jre-8u20-windows-i586-iftw.exe
Doing so will produce the server issue of the server has not found anything matching the requested URI / Uncompression of download file failed (see attached screenshot)

Note that there is no such issue if going from
9 ---> 8u20
8u11 --> 8u20

just the very issue from 8u25 --> 8u20
(not sure if it also impact other upgrade/downgrade but the above scenarios tried and proven)