How do I find JEDEC registered specifications?
As mentioned by Whit3rd in the answer of What is actually a standard part?, JEDEC manages a list of device registrations of electronic components. For example, 1N400X diodes were originally developed by Motorola, but registered at JEDEC as a generic part number, and its specification is published in ELECTRON DEVICE TYPE REGISTRATION RELEASE NO. 4190C (FINAL). 

Unfortunately, the information is not published at the official website of JEDEC, and is only accessible via third-party vendors with payment, thus it's difficult for the general public to learn anything at all from them - a too common problem in many industrial alliances! 

But I recently found a shortcut. It only occasionally works, but it does sometimes provide you some of the information in JEDEC specs without payment, it's not satisfactory at all, but better than none, I guess. The secret is: some manufacturers occasionally cite the original JEDEC specs in their own datasheets. For example, using 1N400X diodes as an example, if we take a look at ON Semiconductor's datasheet, we see a small footnote:


  † Indicates JEDEC Registered Data


And if we review the datasheet again, looking for the "cross" symbol...



So, in this table, all the data listed in Peak Repetitive Reverse Voltage, Non−Repetitive Peak Reverse Voltage, RMS Reverse Voltage, Average Rectified Forward Current, and Non−Repetitive Peak Surge Current came from the original JEDEC specs of the 1N400X diodes. 

There in an additional table with this symbol as well...



So we can assume that everything listed in Electrical Characteristics is data from the original JEDEC spec as well. But be careful here: all the parameters listed here are maximum ratings, thus only the MAXIMUM values given here are valid JEDEC specs, not TYPICAL values. To verify this fact, I paid to get the original JEDEC spec and crosschecked it. 

In conclusion, this method suffers severe limitations: you can only occasionally found them in datasheets of various vendors, you cannot access the primary source and never verify the data is correct, and you must ensure the part number offered by the vendor is identical to the JEDEC part number and not to be confused it with a myriad variations and modifications of the original part.

But it does prove that JEDEC specs, in fact, exist. And it allows you to access some numbers without payment. I guess you can even cross-verify the datasheets from different vendors for hunting.