Lots of factual questions can be answered with 100% certainty by referring to the NLI home page:
http://www.nationalletter.org/
(NLI signing dates are here. This is when the NLI is “issued” as you put it)
Here are the NLI schools:
http://web1.ncaa.org/onlineDir/exec2/nliListing
Lots of other helpful info too