From the Nunes memo ...
Sally Yates, then-Acting DAG Dana Boente, and DAG Rod Rosenstein each signed one or more FISA applications on behalf of DOJ.Combine that with the approximate dates of each of the four applications ...
October 21, 2016 was the first. The others follow on approximate 90 day intervals. So roughly, January 21, 2017 is the next one. Yates was fired January 30, 2017, so Yates probably signed the second one. That would leave one each for Boente and Rosenstein.
If Yates didn't sign the second application, Boente did, shifting the question to "how many FISA warrant applcaitons did Boente sign?" Or, more particularly, did Boente sign the third FISA warrant applcation, or did Rosenstein?
Boente assumed the role of Acting AG when Yates was fired. The third FISA warrant applcation would have been due around April 21, 2017. Rosenstein was not sworn in as DAG until April 25, 2017.
Another way to derive "who signed" is to view the FISA warrant applicaitons, redacted though they be, the approval signatures are in place, with month and year visible, day of month redacted.
Yates - Oct 2016 (page 65 of pdf)
Yates - Jan 2017 (page 161 of pdf)
Boente - Apr 2017 (page 271 of pdf)
That's three out of four, same result reached by cross reference of Nunes memo with "swear in" dates of DOJ signatories.
Thanks, I stand corrected.
I just wrote from my memory, apparently it is flawed.