Did a test build for JDK 1.5.0_01 using JDK 1.5.0 master workspaces with UPDATE_VERSION set to 01. Here is the commands I used for source bundle generation:

cd <workspace>/control/make
gnumake source MILESTONE=rc BUILD_NUMBER=b63 ALT_OUTPUTDIR=<output_dir> UPDATE_VERSION=01

After the soruce bundle generation is done, I got the following source bundles:

internal.zip
java_plugin-1_5_0-rc-src-b63-windows-06_aug_2004.zip
javaws-1_5_0-rc-src-b63-06_aug_2004.zip
jdk-1_5_0-rc-bin-b63-scsl-06_aug_2004.zip
jdk-1_5_0-rc-src-b63-linux-06_aug_2004.zip
jdk-1_5_0-rc-src-b63-scsl-06_aug_2004.zip
jdk-1_5_0-rc-src-b63-solaris-06_aug_2004.zip
jdk-1_5_0-rc-src-b63-solwin-06_aug_2004.zip
jdk-1_5_0-rc-src-b63-windows-06_aug_2004.zip
jre-1_5_0-rc-src-b63-linux-06_aug_2004.zip
jre-1_5_0-rc-src-b63-solaris-06_aug_2004.zip
jre-1_5_0-rc-src-b63-solwin-06_aug_2004.zip
jre-1_5_0-rc-src-b63-windows-06_aug_2004.zip

Note all bundle names still have 1_5_0, not 1_5_0_01.