E1EDKA1 - LIFNR and PARTN

After doing a lot of trial and error with EDI and IDocs, I'm in desperate need to validate my findings. Specifically, I am concerned with the difference between the fields PARTN and LIFNR in segment E1EDKA1.

Talking about incoming ORDERS, my understanding is the following:

1. The customer knows under which number he is stored in my system:
-> He submits this number in PARTN

2. The customer doesn't know my internal number:
-> He sends his number in LIFNR
-> I need to maintain a mapping in table EDPAR - VOE4 to determine the corresponding internal number

3. Concerning E1EDKA1 LF (supplier):
No need to differentiate betweend known and unknown number.
-> Customer sends the number he uses for me as a supplier in PARTN.
-> I maintain an entry in table EDSDC - VOE2 using exactly this number.

Could you please give me a feedback, if I'm handling this the right way? Is this how it is intended by SAP?

Thanks in advance.