Neville Hillyer wrote:
. . .
In the spirit of exchanging ideas I would be grateful if you could say why so many historic MA documents appear to mislead in that they often fail to mention that MA needs to be used at both ends.
They don't mislead; it's not always required, as you'd know by now if you would actually read the posts here, and/or the Apple articles, and/or How do I set up a new Mac from an old one, its backups, or a PC?
For example, the article you linked to (http://support.apple.com/kb/HT4413, for Snow Leopard):
You always need either Setup Assistant or Migration on the target (new) Mac, if you want an automated transfer. That should be clear from the title and the summary section. (Unfortunately, the difference between Setup Assistant and Migration Assistant isn't made clear until the Additional Information section at the very end.)
You also need Migration Assistant on the source (old) Mac if you're transferring via network.
The article in question has several sections, where that's made crystal-clear:
• FireWire
• Ethernet
• Wireless
• Time Machine backup or other disk.
The FireWire section walks you through connecting via FireWire and starting the old Mac up in Target Disk mode. No mention of Migration Assistant on the source Mac, as it's not used.
The Wireless or Ethernet section walks you through connecting, then (step 8) says to start Migration Assistant on the source Mac, and steps 9-12 show how to establish the link.
The Time Machine or other disk section walks you through connecting and selecting a TM or other disk, or TM backups on a Time Capsule. No mention of Migration Assistant on the source Mac, as it's not used.
Another instance of this is the assurance during installation that MA can be used later to import data. Clearly from what you say this is not always possible.
Sure it is. It's just better to use Setup Assisant when the new Mac first starts up, as doing it later with Migration Assistant means you'll have at least one extra user account (which confuses folks), and the transferred accounts may lose permission to files on other disks, especially TM backups, as detailed in the blue and pink boxes in Problems after using Migration Assistant (also linked to from the main How do I set up a new Mac from an old one, its backups, or a PC? article).
And yes, several of us have asked Apple to change that wording, to no avail so far. Please feel free to add your voice here: http://www.apple.com/feedback/macosx.html
In particular it is not possible if the old OS is unable to boot.
If it's totally unable to boot, yes, of course. But if it won't start OSX, it may boot in Target Disk mode, so unless there's also trouble with (or on) the internal HD, you may be able to transfer that way.
Or, in any case, if you have Time Machine backups on a Time Capsule (and in some cases other network locations), or "clone" backups on an external HD, you can transfer from them (per that section).
Could there have been an earlier type of MA which was single ended?
They're all "single ended" if you transfer via FireWire, Time Machine, or other disk.
If so this could, to some extent, be the explanation for some documents being wrong or incomplete.
Again, they're not incomplete on that point.
Do you know when MA was first used?
There's an old version for transferring to Panther or Tiger, per the links supplied in How do I set up a new Mac from an old one, its backups, or a PC?
If you have more questions, I'll be happy to discuss them, but only after you've actually read and considered the Apple articles and/or (preferably and) my web pages on the subject. Start with How do I set up a new Mac from an old one, its backups, or a PC? and follow the appropriate links.