If it was done by EVSEupgrade I believe they all put a different sticker over the amperage nameplate.
If EVSEupgrade, they changed quite a bit over the years, some stopped at 16a and some at 20a. If yours has a L6-30p it's probably a 20a 240v upgrade but even older upgrades with the L6-20p would also charge at 20a on Leafs with the 6.6kWh built in charger.
If it were me I'd simply plug it into the proper outlet and do a amp reading on what your getting, 20a should be the max but could also be 16a. Note if a old EVSEupgrade it might also give you 20a @ 120v(if you have a 6.6kwh Leaf) so keep that in mind if plugging into a standard 120v outlet. Older Leafs only charged at 16a @ 240v and 12a @ 120v. What year and model is your Leaf and do you know if it has the "charger" package?
Never mind, reread your post, and '11 will only charge at a max of 12a @ 120v and 16a @ 240v, no matter how high your EVSE goes.
2012 SL purchased used 2/'16
2013 S w/QC purchased new
Juicebox Premium 60a L1/L2 EVSE, Ebusbar 16a L1/L2 EVSE
'12 EVSEupgrade'd 20a L1/L2 EVSE, '13 EVSEupgrade'd adjustable 6-20a L2, 6-13a L1 EVSE
Zencar 13, 20, 30a L1/L2 portable EVSE
GE Durastation 30a