I just have trouble understanding how something can be 'introduced' without being actually available...
I know, sometimes it's difficult to know just where to draw the line. Being just an amature, not a 'real' historian, I can only use my own judgement, based on the 'preponderance of the evidence' (hey, it's good enough for the judicial system, where I've done my civic (jury) duty twice now). Of course, I can't always get it right, so that's why I usually try to use such qualifiers as 'widely recognized', 'said to be', etc (I've even been known to use 'rumor hath it', for very obscure factoids).
I do try and do as much research as possible, but, as you point out, sometimes it's difficult to find authoritative (first-hand) sources, so we go with what we have available, even when confronted with conflicting information.
Arguably, the GRiD Compass could be considered the 'first' laptop, as it was designed as early as (1979?), although it was not produced until later.
Just for the hell of it, here's another source of (mis?)-information:
http://inventors.about.com/library/inventors/bllaptop.htm Caution...here be many popups...
--T