To make sure one thing about Bussine Add-In

I have searched many information on the net,and saw many blogs about BADI.But there is a doubt,just like the following screenshot:

Just as the blog said"The Business Add-In enhancement technique can only be implemented once", but I take a BADI "QEEM_SUBSCREEN_5000"

for example. And at least I do twice to implement it and it doesn't report any errors, just like the data in the table SXC_CLASS as the following screenshot:

Do I understand it wrong??

Can anybody help me ?

Thank you so much.

(comment:My english is poor,if you find any grammer mistakes,please never mind! O(∩_∩)O~)