The 17 berry reverse (D1 reverse) refers to 1921-P Morgan Dollars with a reverse type that includes an "extra berry" on the right side of the wreath not found on most 1921-P reverses, which are also known as the 16 berry (D2 reverse) reverse types. All 1921-P VAM-1 and VAM-1 subvarieties have the 17 berry reverse, plus some other 21-P VAMs in the higher number ranges.

17 berry reverse:

Sometimes the 17 berry reverse coins are associated with the "Zerbe dies", which had 17 berries. However, there are many other 17 berry reverses that do not have other features from the known Zerbe proofs. Click on the Zerbe dies link for more information.

Compare to 16 berry reverse:

17 berry reverse 21-P Morgans sometimes show a small die scratch between the final "t" in "Trust" and the eagle's left wing. Look to the bottom right of the "t":

17 berry reverses also show scribbling lines in the top arrowhead (not to be confused with "scribbling scratches tailfeathers," which refers to a different concept). If you ever wondered if these lines varied from VAM to VAM, they don't. The proof is shown below (if you do find one with a different pattern of arrowhead lines, please speak up). These seven are examples of the scribbling, but all 17 berry reverses should show the same:

These lines are incuse and thus were cut into a hub rather than a die. Since they don't vary from die to die, they would have been a characteristic of the master hub. We can likely identify this "scribbler" as George Morgan himself.

1921-P VAM-1E:
1921-P VAM-1i:
1921-P VAM-1S:
1921-P VAM-1AO:
1921-P VAM-1AQ:
1921-P VAM-15:
1921-P VAM-41:

It is also important to note how the upper arrowfeather meets
the olive branch, in photographs this may be the only way to
tell the two hubs apart. This is the D1 or 17 berry hub.
The top feather joins the branch at the center talon( which
is also doubled on the hub). Compare with the D2 below.

D2 or 16 berry hub. Note how the top feather ends
away from the center talon and now there is a lump on the olive
branch. Counting berries can be deceiving, but this feature will
positively confirm an attribution of which hub was used.

Please click this link for the full definitions page.