I asked Barney Gaylord (MGAguru.com) about the "missing" MG-TE. Here's his suggestion, which sounds at least as probable as the HowStuffWorks "tee-hee" idea:
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Tom,
I have a reasonable guess, but its roots go back to the1952 Le Mans race. See here:
http://mgaguru.com/mgtech/variants/pics/umg400.jpg
This car was EX-172. This is not an MGA, but is a one-off rebodied MG TD built by Syd Enever to run at Le Mans in 1952. The success of this car led to MG immediately whipping up a new production prototype.
See EX-175 prototype.
http://mgaguru.com/mgtech/variants/vt101_ex175.htm
In1952 this was a prototype for a model intended to replace the TD. It did not yet have a model name. It had the XPAG engine from the TD (before the Austin -series engine was available), and same suspension parts as the TD.
There were also a couple more prototypes for successor to the TD. See here:
http://mgaguru.com/mgtech/variants/pics/concept1.jpg
http://mgaguru.com/mgtech/variants/pics/concept2.jpg
Any one of these may have been intended to be the TE model.
But as fate would have it, BMC had just commiitted to build the Austin Healey 100, with lots of investment money involved (and not wanting to compete with itself with a similar model sports car), so the next MG sports car had to be put on indefinite hold. The result was a warm-over of the TD to create the TF model. What else could they call it when it was only a slight modification of the prior T-type model? My best guess is that the TE model name was skipped (in the public domain) because it really did exist, but was never released for production.
Also the MG Z-Type Magnette was on the market by 1953, and they had run out of alphabet, so it would follow to call the latest slight modification to the TD another T-type, therefore naming it TF.
When the new MG sports car did finally hit the market in 1955, and they had run out of alphabet, it was decided to start over at beginning of the alphabet and "call it MGA", then advertising the radical new model as "First Of A New Line". The proper model name is MG "Series MGA" (never called 1500) which was followed by Series MGA Twin Cam, Series MGA 1600 along with Series MGA Twin Cam in 1600 body style, and Series MGA 1600-MK-II". Each of these 5 models also had a Coupe variant (5 more models).
When the Twin Cam was discontinued, some TwinCam chassis parts were already contracted for, so those parts were used by installing pushrod engines in the Twin Cam chassis. That ultimately created 4 more unique models. We call these "Deluxe" (although the factory never used that name), which came in 1600 and 1600-MK-II both roadster and Coupe form. Interesting bit here is that there were 4 uniquely different body shells procuced for only 360 of the "Deluxe" cars. All totaled it makes 14 different models of MGA in 7 years of production.
Food for thought,
Barney Gaylord
1958 MGA with an attitude
http://MGAguru.com