I think the DP22 decal was used when a machine was upgraded to 10 cents from 5 cents. The decal was a little more prominent and they wanted to insure that customers knew of the price change since coins could not be retrieved once inserted into small door mechs. I mainly see them on early 50's uprights like the VMC-27/33.
The DP21 decal could be used on a large door mech machine or one with with an electric mech. Again probably used to alert customers of the price increase with a prominent decal.
I have a Vendo five cent change giver mech for a small door on my V-81B, but no none reproduces the correct decal so not every combination may be available...
Jim - I got Steve Ebner to print a sheet years ago. I think if Janet dug around a bit, she would find she has a few left as I recall 50 were on a sheet. I bought about 10 of them and have 6 left, but they are paired with the change-givers I have. I could possibly have an extra, but I'll have to check my 39 in the shed and see if I have a change-giver installed in it. If not, then I have an extra.