Bases loaded home runs, aka, grand slams.

I'm working on data, trying to find the number of at bats (AB) with the bases loaded that Lou Gehrig and other old timers had.  Gehrig supposedly has the record: 23 home runs with the bases loaded: grand slams.  Knowing the number of opportunities would add vital context to that record.

It seems that Gehrig's record has been known for a very long time but how did anyone know it was a record way back then and whose record did Gehrig break?  Babe Ruth, who had 16?

Baseball Almanac has a list of Gehrig's grand slams.  However, it does not indicate the source of that data.  Nor do any other places that I checked including the official Lou Gehrig website, wikipedia, SABR bio.

Alex Rodriguez recently hit his 22nd home run with the bases loaded.  Rodriguez has a much better home run rate (AB/HR) with the bases loaded than overall: 9.6 to 14.3.  Lower is better.  So does Manny Ramirez who is third with 21: 11.3 to 14.9.  Ramirez recently retired.

The Tattersall- McConnell home run log has details supposedly on all MLB home runs.  However, it does not explicitly include AB for bases loaded home runs.  For modern players I can find that in:

http://www.baseball-reference.com/

and

http://www.retrosheet.org/  OK, I can't actually find the Gehrig home run log there but I can't find lots of stuff at retrosheet.

Bob McConnell appears to have started his research in the 1950s.  It's unclear when John Tattersall started his research.  Did Tattersall or McConnell discover Gehrig's grand slam achievement or was it already known and, if so, how?

Gehrig's home run log in baseball-reference indicates that his very first grand slam on July 23, 1925 bounced into the stands at Yankee Stadium under the old rule (fair balls bouncing into the stands were home runs) that was eliminated after the 1930 season.  That means that in a real sense Rodriguez has already tied Gehrig.  Gehrig's only other bounced home run was July 30, 1927 with the bases empty.

Gehrig hit 10 inside the park home runs (IPHR); one was a grand slam: July 5, 1934 at Yankee Stadium.  Rodriguez has no IPHR.