With version prefix and revision like in example _service below:
 <services>
  <service name="tar_scm">
    <param name="scm">git</param>
    <param
name="url">https://git.chromium.org/git/chromiumos/platform/vboot_reference.git</param>
    <param name="versionprefix">git20170302</param>
    <param name="filename">vboot</param>
    <param name="revision">a1c5f7c006b7bb3d5894f132f70ba3bbadfd9d6b</param>
  </service>
 <service name="recompress">
    <param name="file">*vboot*.tar</param>
    <param name="compression">bz2</param>
  </service>
  <service name="set_version"/>
</services>
resulting set_version version is 64.
Removing 'git' string from version prefix and using short hash in revision,
like below, fix
problem and produce correct package version.
<param name="versionprefix">20170302</param>
<param name="revision">a1c5f7c</param>