Sorry, I seem to have missed this thread also.
The deal with ATEUPD is that it is really intended to be customized by dealers. The source code is available, in [901,2] of the SOSLIB, and the min/max versions are set in a Procedure called Get'Min'Max'ATE'Requirements.
My thought was that any dealer/developer who wanted to use this mechanism for updating would take ATEUPD, and modify that routine, possibly to get its inputs from some external source, so that you could control what range of versions you wanted your clients to be able to use.
Of course, being able to set your own min and max versions doesn't do much good unless somebody maintains one or more of those versions online. Our Update Center repository only maintains one version right now, so it would be best for you to maintain your own Update Center repository. (All you need is some web-visible storage and a copy of the Update Creator from Firmaware to maintain it with.)
As for updating from 5.0 to 5.1, by default, ASHUPD only updates within the major.minor series that you are in, but you can override that by using the /V:51 switch. ATEUPD needs a little more work to support a similar capability.
Another possible route for updating ATE clients is to use the original method of putting the installer package in the %MIAME%/atesetup directory of the server, where each ATE client will recognize it and offer to update. The main 2 downsides of this approach are:
1) The installer asks too many questions, allowing the user to do things beyond merely updating with the original configuration.
2) The install package is several MB, making it possibly slow to download from the server to the client, if connecting over a remote link.
The new SetupBuilder installer offers potential improvements in both areas, although we haven't really exploited them, other than to auto-detect the existing installation and offer/default to just update it. Depending on interest, we may add a switch to force it to only update, with no questions asked, and possibly to start with a mini-installer which can then grab the rest of the pieces from the web.