In my estimation from many years following the markets on a wide variety of transferable MGs, the number of fully transferable Ithaca grease guns in the NFRTR is very, very small. Obtaining numbers of specific models of grease guns is impossible at this point in time, but it is clear to me that there are many more pre-May samples of Ithacas than transferables. The overwhelming majority of grease guns are Guide Lamp guns. Ithaca manufactured comparatively few grease guns.
I don't count the Medea repro grease guns as part of this issue.
Very slowly ATF/NFA is working at cataloging the numbers of specific models of different types of MGs in the NFRTR but there are major hurdles to this endeavor due to the way that MG ID and serial registration information was handled since 1934. Many longtime collectors, dealers, etc have fairly accurate compilations of the numbers of some vintage MGs in the NFRTR. The numbers and types of pre-'68 MGs In the NFRTR are the most difficult to filter out.
The importation of M3/M3A1s post-WWII by GIs as well as importation prior to and during the DEWAT retail burst in the mid 1950s was considerable and many of these wound up being registered before or during the '68 Amnesty. That was just good luck.
Others might have some ideas about this as well.FWIW