On 2010 Dec 17, at 11:13 AM, Shoppa, Tim wrote:
   They are
interesting, but no more than weird numbers on semicustom
 devices. Motorola does the same thing, with their SC series of parts
 (not MC or XC).. 
 I tend to come in on this side too, these funny series are
 Effectively TI-supplied "house numbers".
 They may be different than stock SN7400 TTL or whatever DTL in minor or
 Major ways but that was an agreement between the customer and TI.
 I've seen the innards of DTL and TTL based calculators, and to think
 that
 They would work with rejects or floor sweepings is unreasonable. If
 Anything I would think that the house-numbered part would have some
 specs tightened
 And others loosened to produce something most manufacturable. And isn't
 That the reason for house numbers to begin with? (e.g. not purely
 obfuscation) 
 
I kind of thought that was what I was getting at when I first suggested
they might be a consumer-grade version of standard parts. No, they're
not going to stoop to using rejects (nor would TI put their logo on
them if they were, as William said), but the speed, temperature range,
etc. requirements for a desktop calculator are not that high. Low cost
is a requirement, and selecting something more manufacturable  may well
help that.